When Rhianna Chellew was diagnosed with an inoperable brain tumour, her eight-year-old friend wanted to do something for her.
Kobi Barrow set about raising money for a park where disabled and able-bodied children could play together.
After he raised £85,000 a new park is to be opened in Neath in memory of Rhianna, who died in 2016.
"I hope she's looking down and watching us", said Kobi, now 10.
Rhianna, from Swansea, was just 36 hours old when she was flown from Wales to Scotland in a huge transporter plane for life-saving treatment.
Her life was saved and she astounded doctors by being well enough to go home at three weeks old.
But, in April 2015, her family was given the devastating news that she had cancer.
She died just over a year later.
The park can be used by both able-bodied and disabled children, including those that are more severely disabled and who use wheelchairs.
Kobi came up with the idea because Rhianna had to travel about three hours to use a park in a wheelchair.
"I feel great that people like me and people like Rhianna can come here to play together," he said.
"I've had loads of happy memories in the park, so why can't she have any?".
"Rhianna was a kind person," he said.
"I still have the memory of when I met her of how much we played and everything that happened with me and her.
"I hope she's looking down and watching us."
Johnny, Rhianna's father, said the park opening was particularly poignant as it fell on the week marking two years since her funeral.
"It's always hard," he said. "But this part is something that Rhianna would have wanted.
"She's definitely left her mark on the world with this park. We are just so proud of her."
Kobi's dad, Marc Barrow, who is chairman of Rhianna's Swing added that many families had been in touch saying they will bring their children to play at the park.
"It's been two years in the making and its so nice to see the end product," he said.
"Who knows, we may build another in Swansea."