A group of teenagers with haemophilia who were infected by contaminated blood made a pact that whoever survived would find out what was killing them, a public inquiry has heard.
Stephen Nicholls, now 52, said he is the only one of his friends left alive and he thinks about that "every day".
Thousands of people were infected with hepatitis C and HIV from contaminated blood in the 1970s and '80s.
Victims are telling a public inquiry how their lives have been ruined.
Prime Minister Theresa May said the public inquiry into the contaminated blood scandal "should have taken place earlier".
Mr Nicholls was diagnosed with haemophilia when he was one.
At the age of eight, in 1976, he started attending Treloar's school for children with disabilities, in Hampshire.
He was one of 89 boys at the school with haemophilia, who were offered treatment onsite.
But, the inquiry heard, only 16 were alive today and, among his group of friends, Mr Nicholls was the only survivor.
He said: "It was my last year at a school when the first haemophiliacs were starting to die - and everyone was really scared.
"We realised that 'this is really serious' and 'this is killing us' or 'killing haemophiliacs'.
"There were four or five of us in a room and we said, 'This is going to happen to us, we can see it.'
"We said, 'Right, we've stuck together right through our childhood. If it happens and it kicks off, we're going to rely on the person still alive to pursue it and find out why and what went wrong.'
"I'm the only one left. That's tough. I think about that every day."
'I could be next'
Mr Nicholls, from Surrey, said: "We're a tough bunch.
"We ate together, we learned together, we were treated together. We became like brothers.
"To see your friends dying one by one, it's always in the back of your mind, 'I could be next.'"
Mr Nicholls was diagnosed with hepatitis C in 1991.
As part of the inquiry, the treatment given to pupils at the school is being investigated to see if they were given contaminated blood products.