Robert and Trude mourned what they thought had been a lonely and isolated life for their disabled son. But when Mats died, they discovered that people all over Europe lit candles in his memory.
A version of this story was first published in Norwegian by broadcaster NRK.
"We were really very traditional. We didn't want him turning his daily rhythm upside down."
Sitting in a cafe by his office at Oslo City Hall, Robert Steen describes how he used to worry about his son staying up late into the night.
"In retrospect, I think we should have been more interested in the game world, where he spent so much time," says 56-year-old Robert. "By not doing so, we robbed ourselves of an opportunity that we didn't know we had."
Robert delivered his funeral eulogy for Mats in late 2014, in a chapel at the Norwegian capital's Western Cemetery.
Among those who sat listening to his words - in-between relatives and a few people from the health service who knew Mats well - was a group of people the family didn't know.
Only Robert had met them. And only once, the evening before.
Mats had barely left the basement flat underneath his family's home in the last years of his life, so it was strange that people unknown to the family were present at the funeral.
Even stranger - Mats himself had also never met these people.
Before his death, these grieving visitors would not have thought of Mats as Mats - but instead as Ibelin, a nobleman by birth, a philanderer and a detective. Some of those paying their respects lived close by, but others had come from afar. They wept for their good friend.
Later in the funeral service one of them would speak, and tell the gathering that just now, all across Europe, people were lighting candles for Mats.
It was written in the stars, it was coded in his DNA.
The Mats that sauntered around with a crown on his head on his fourth birthday in July 1993 would, within a few years, not be able to walk.
Robert and Trude had received the news in May 1993, in a small office in the large brick building that houses Ulleval Hospital.
Mats's parents learned why their boy kept falling off the swings and hurting himself, why he didn't climb up the ladder on the slide at the nursery, even though he loved to slide down, why he supported himself on his knees like an old man when he rose from a sitting position and why he didn't race the other children.
The doctors told Robert and Trude that Mats had Duchenne muscular dystrophy (DMD), a rare disorder that causes muscle degeneration - mostly in boys. Mats's genes contained a coding error that would prevent his muscles from developing normally. And which would finally destroy them.
"After we put Mats to bed that evening we called the doctor. We had been given permission to do that. We could call any time, if we needed more information," says Robert.
With Trude sitting by his side, Robert spoke on the phone for more than half-an-hour.
"I said to the doctor: 'But at least he won't die from this!' The doctor on the other end of the line was silent for a moment, 'no, but our experience is that these patients rarely live to be older than 20'."
"He managed to make it to 25."
At the family home in Ostensjo in south-east Oslo, Robert and Trude tried to take it all in.
Mats would not live what they considered a "normal life". He would die young and be taken away from them - without having set his mark on the world.
They were so completely mistaken.
If our DNA maps out our lives even before we are born, how can we choose who we want to be?
Mats found a way and created himself anew.
By the turn of the millennium, the Steen family had moved to a wheelchair-adapted home in Langhus, to the south of Oslo.
While Mats was allowed to play his handheld Game Boy during breaks at school, not even Super Mario could chase away the feeling of being different. Mats sat in his wheelchair and an assistant went with him everywhere.
His parents wondered what activity Mats might like to do in his spare time - when his classmates were playing football and running around outside.
Online gaming perhaps? Robert gave him the password to the family PC, and a new world opened up for the 11-year-old.
"In the course of the last 10 years of his life, Mats played between 15,000 and 20,000 hours," Robert said in his eulogy. "That's equivalent to more than 10 years' full-time employment."
But the gaming also caused family friction.
"When the night nurse arrived at 22:00, Mats had to be in bed," says Robert. "Their job was to monitor Mats in bed, not to put him to bed. Mats protested but reluctantly agreed."
Mats had become a gamer. Gamers don't go to bed early.
So who was Mats during all of those hours he spent playing?
He became Lord Ibelin Redmoore and sometimes Jerome Walker. "Jerome and Ibelin are extensions of myself, they represent different sides of me," he wrote.
He immersed himself on the planet Azeroth, in the hugely popular game World of Warcraft. Azeroth is a mythical fantasy world. There are continents, seas and forests, cliffs and plains, villages and cities. Mats spent most of his time in a region called the Eastern Kingdoms.
As an online player you get to know this world bit by bit, just as you know your physical world.
There will be places you plan to travel to, and landscapes and cities you will master - some better than others. In some areas you will be on your guard, while in others you will love to hang out. You will find your local inn and meet new, interesting people.
That's the way the world is. That's the way Azeroth is.
Mats made the journey and found a wide circle of good friends.
"When I went past Mats's basement flat during the day and the curtains were closed. That is a sorrow I remember well," says Robert, who works as Oslo's vice-mayor of finance.
"'Oh, no,' I thought, 'he hasn't even started his day yet'. I was sad because his world was so limited."
But non-gamers don't see the whole picture. They don't realise it's more than just shooting and point-scoring.
"We thought it was all about the game. And just that. We thought it was a competition that you were supposed to win."
And there was the matter of Mats's circadian rhythm - his 24-hour daily cycle.
"We didn't understand why it was important for Mats to be online late in the evening and at night," says Robert.
"But of course, it isn't in the morning or in the middle of the day that people are playing. That is when most of them are at school or work.
"We first understood it after he passed away. Until the very end we wanted him to be asleep by 11 at night, like other 'normal' people."
Lisette Roovers, from Breda in the Netherlands, was one of Mats's close gamer friends. She was also one of those present at the funeral in 2014.
She is in Norway again - visiting friend Kai Simon Fredriksen, who also played online with Mats.
"I knew Mats for many years. It was a shock when he died, and it has shaped me," says Lisette, sitting on Kai Simon's sofa in Hoybraten, in north-east Oslo.
Lisette, now 28, was only 15 years old when she met 16-year-old Mats. Or, to be precise, when Lisette's game character Rumour met Mats's game character Ibelin.
"We met in Goldshire," says Lisette.
"It's not a nice place any more, but back then Goldshire was a pleasant little village, where you could meet new, interesting characters. I was looking for someone to role play with, and among others sitting around a campfire was the one I would later learn to know as Ibelin.
"I - or Rumour, rather - acted somewhat impulsively. I jumped out of the bushes and snatched Ibelin's hat. We stood for a moment, staring back and forth, then I ran away with his hat, with no thought of direction."
She smiles a little.
Mats also wrote about this first meeting with Lisette, in a blog post he called Love.
"In this other world a girl wouldn't see a wheelchair or anything different. They would get my soul, heart and mind, conveniently placed in a handsome, strong body. Luckily, pretty much every character in this virtual world looks great."
Lisette says: "Mats was a good friend, sometimes a very close friend.
"We wrote [to] each other about everything, but he didn't write about his condition. I thought his life was like mine. For example, we were both agreed that we hated school."
But there were things on which they could not agree.
"He wrote that he hated snow. I wrote that I loved it. I didn't understand then that he hated it because of his wheelchair. I didn't know about it."
Teenage Lisette's love of gaming concerned her parents. They were worried about her school studies and her apparent lack of a social life. Their solution was to restrict her access to online play.
"Being separated from my game friends was hard for me," Lisette recalls.
But Mats did not fail their friendship. Even if he could not find her in the game, he kept in touch with her through other channels.
"He even wrote a serious letter to my parents, in which he tried to help them understand how important playing was for me," she says. "I have saved that letter."
Robert and Trude knew their son wrote to someone named Lisette.
"Mats spoke quite a bit about these game characters - these avatars - but we didn't think much of it. He told us about Rumour, among others," says Robert.
"She, or Lisette rather, sent him presents, including on his birthday. We thought that was touching, and we also teased him a bit about it. Then he blushed, really blushed.
"So we thought of Lisette as a friend, because of these presents. They were tangible proof of real friendship, you could say.
"We didn't call the others he was in touch with, friends. We called them avatars. Our perception of friendship was very traditional."
In World of Warcraft, you can either play alone or join forces with other players and form a group - or guild. Mats was part of such a group, Starlight, with about 30 members.
"Nobody just becomes a member of Starlight," says Robert, now educated in the ways of the World of Warcraft. "To become a member you have to be recommended by someone who is already on the inside, then complete a trial period of one to two months."
Starlight has existed for more than 12 years and is still an active group.
"Starlight is a special group, because it has remained united for so long. That is probably why friendships in Starlight go so deep," concludes Robert.
Forty-year-old Kai Simon or Nomine, as he is called in the game, is the leader of Starlight.
Every year since Mats's death in 2014, Starlight has held a memorial to share memories of their comrade.
Last year, Kai Simon told other group members that when remembering Lord Ibelin Redmoore, they should focus on running and swimming.
"Ibelin was a runner," Kai Simon explains. "It was important for him to be able to run, and it was important for him to be able to share the experience of running with others."
Is Kai Simon now talking about Mats, or about Mats's game character? Maybe it doesn't matter. Maybe this is how it was. The person and the character became one.
In the summer of 2013, Mats was 24 years old. The Steen family were on holiday in Majorca, while Mats - unable to travel - stayed at home in his basement flat with his assistant.
Mats had to have someone with him at all times. Through the years he had a number of different personal assistants - including his uncle. Luckily for Mats, some of the assistants were also interested in gaming.
While his parents were away in Spain, Mats started his blog "Musings of life". In a post titled "My escape", he wrote about life in Azeroth.
"There my handicap doesn't matter, my chains are broken and I can be whoever I want to be. In there I feel normal."
Mats shared his blog with the members of the Starlight guild - one by one. This was how they got to know about their fellow player's offline situation.
Lisette recalls the first time she read the blog.
"I was floored. And I got a bad conscience because I had occasionally teased him in the game and had not always been totally considerate.
"Then I thought, 'Do I have to start behaving differently towards him from now on?'. But I decided to treat him just the way I had before. He also wrote in his blog that this is what he wanted."
In online play, she is Chit - a rough and ready character. Offline, she is Anne Hamill, a 65-year-old retired psychologist from Salisbury in the UK.
Anne says she finds it fascinating how the Starlight group functions for those who often fall by the wayside in the offline world.
"Because we meet each other without preconceptions, Starlight feels safe. Even for those who see themselves as outsiders.
"Online play is a fantastic arena for meeting people and building friendships. We discover each other without stereotypes in the way. It provides the chance to find out if we like someone - and only then reveal our age, gender, disability or skin colour if we feel like it.
"I think Mats was lucky to belong to our time, technologically," she adds. "In Starlight he was a key member. If he had been born 15 years earlier, he wouldn't have found a community like that."
About six months before he died, Mats was absent from the World of Warcraft for 10 days. His fellow players wondered where he was.
"Ten days was a very long time to be logged off, because Mats was always there, when you needed someone to play or chat with," says Anne.
When he returned to the game, the others learned that he had been admitted to hospital. Anne says she finally decided to say, in game chat, what she had been thinking.
She wrote: "Mats, you must give someone a possibility to come into contact with us, if something should happen to you. So that we can know, even if you can't give us a message yourself."
She hoped he would either give his password to someone, or come up with his own solution of how to let Starlight know if something had happened to him.
"You are important to us," she wrote.
"You are just saying that because you have learned that I am sitting in a wheelchair," replied Mats.
"I told him that wasn't true," says Anne. "I said, 'you are important to the guild. You are a fantastic listener. You are one of the people who lifts others up in Starlight'."
It was a while before Mats posted again.
"I really understood then, that he had taken what I had said to heart."
On 18 November 2014, Mats died.
Critically ill, he had been admitted to hospital. Doctors managed to stabilise him and said he could soon be allowed home - but then the family were told to come as quickly as they could.
"He was on the fourth floor at the end of a corridor. Every second was precious, the corridor was so long," says Robert.
They came too late.
The photograph Robert took of his son on his deathbed shows a pale young man, with dark wavy hair. He has finely drawn eyes, a noble nose and a mouth marked by the breathing mask he had used for so long. He looks like he is asleep.
Many years before, Lisette had made Mats a drawing. Ibelin is holding Rumour, a scarf conceals his nose and mouth.
"Mats got it through the regular mail," Robert says.
"Now it is hanging on the wall at home."
The day after Mats died the whole family was at home.
"The doorbell was ringing, flowers arrived, neighbours visited. We cried," Robert recalls.
Robert tried to think who he had to tell about Mats's death. He remembered the gamers and wondered how in the world he could reach them.
"Before Mats died, I never thought that I would have to have his password."
But now he needed it.
"That was when I thought of his blog," says Robert.
In fact, Mats had given his father the password to his blog, so that Robert could continuously check its statistics and monitor how many had visited and read each post.
"You don't know who plays a role in your child's life if you don't know their digital friends," says Anne, or Chit - as she offers some advice to parents.
"Make an agreement with your children about how to reach their digital friends in case anything should happen to them. Otherwise, they may have friends who will go around wondering forever what happened."
At the end of the blog post about Mats's death, Robert posted an email address for anyone wanting to get in touch.
"I wrote and cried. Then I hit publish. I didn't know if any replies would come… and then the first email arrived - a heartfelt condolence from one of the players from Starlight.
"I read the email aloud: 'It is with heavy heart I write this post for a man I never met, but knew so well.' It made such an impression."
Then came more messages of condolence - more stories of Mats's gaming life.
"He transcended his physical boundaries and enriched the lives of people all over the world," read one. "Mats's passing has hit me very hard. I can't put into words how much I'll miss him," said the next. "I don't believe that one single person is the heart of Starlight. But if one was, it would have been him."
Robert says: "An entire society, a tiny nation of people began to take shape.
"And it was on a scale that we had no idea existed. More and more emails arrived that testified about the kind of significance Mats had."
When Mats's group, Starlight, learned of his death, the members pooled money so that those who could not afford it had the opportunity to travel to Norway for the funeral.
Robert says the family was very touched.
"We cried and cried from an intense emotional joy that came from seeing what kind of a life Mats had in fact lived. With real friends, sweethearts, people who cared so much that they would fly from another country to the funeral service of someone they had never met. That was powerful."
Lisette from the Netherlands went to the funeral. So did Anne from the UK, Janina from Finland and Rikke from Denmark.
On behalf of the Starlight members, Oslo native Kai Simon addressed the congregation.
"While we are gathered here today, a candle is being lit for Mats in a classroom in the Netherlands, a candle burns in a call centre in Ireland, in a library in Sweden there is a candle lit, he is remembered in a little beauty parlour in Finland, a municipal office in Denmark, many places in England. All over Europe, Mats is remembered by many more than those who had the opportunity to come here today.
"I met Mats in a world where it doesn't matter a bit who you are, what kind of body you have, or how you look in reality, behind the keyboard.
"There, what does matter is who you choose to be and how you conduct yourself towards others. What does matter is what is found here," - Kai Simon laid his hand on his temple, "and here." Kai Simon laid his hand on his heart.
In his blog, Mats had written about the computer screen which he had sat in front of for over half his life: "It's not a screen, it's a gateway to wherever your heart desires."
Vicky Schaubert works for NRK in Oslo. Read her article in Norwegian here.
Top image: Blizzard Entertainment/Patrick da Silva Saether/NRK