They grew up together in tiny two-up two-down houses in the Lower Falls and the bond between them was unbreakable.
"We lived in number six Peel Street and the Conlons lived in number seven," says Richard O'Rawe.
"Gerry and I were the same age.
"We were inseparable.
"Falls Baths was just across the road and we'd go to the swimmers every day after school.
"We had no baths or hot water at home, so about five of us would crowd together and sit under one shower for ages, lingering in the sheer luxury of it."
That was the 1960s before conflict erupted in Belfast.
"Even as a kid, Gerry was effervescent. He made you feel special when you were with him," his friend says.
He recalls football games on summer evenings in the street lasting four hours - "you needed 24 goals to win a match".
Come winter, the boys would chop up wood and sell sticks around the doors.
They'd shovel snow from old people's doors for 1p.
"That's how working-class kids got a couple of bob back then," O'Rawe says.
A decade later, both men would be in prison.
O'Rawe was there for IRA activity he was involved in, but Conlon was convicted for a bombing of which he was entirely innocent.
O'Rawe has written a book charting his best friend's life.
In the Name of the Son: The Gerry Conlon Story will be launched in Belfast tonight.
"Even though we were best mates, our outlook when the conflict started was very different," says O'Rawe.
"I was born into a republican family.
"I was told about Patrick Pearse before I could talk. Kevin Barry was the first song I learnt.
"A portrait of the 1916 leaders hung on our wall.
"Billy McKee and Proinsais McAirt (Provisional IRA founders) were in and out of our house all the time.
"They were my daddy's friends.
"The Conlons' home was very different.
"Gerry's father Guiseppe was a quiet man.
"But our mothers were alike.
"They were totally opposed to violence and thought only God had the right to take life."
In 1974, 20-year-old Conlon told O'Rawe he was moving to London.
They said their goodbyes over a few drinks in a west Belfast bar.
"I knew Gerry would always end up in London," his friend says.
"He was someone with no politics, living in a war zone
"There were gun battles every day in the Lower Falls and he wasn't up for that.
"He wanted to escape and live life.
"The big smoke was the natural place to go."
IRA Belfast commander Brendan Hughes had also advised Conlon to leave Belfast.
"Gerry was shop-lifting in the town. He was basically stealing to order and the IRA wasn't impressed," O'Rawe says.
Conlon was in London for just a few months when he was arrested and charged with the Guildford bombings in which five people were killed.
He was convicted in 1975.
"I was in jail at the time but knew it was bulls***," says O'Rawe.
"There wasn't an ounce of republicanism in Gerry's body.
"He wasn't IRA material and the IRA wouldn't have taken him anyway." But the republican prisoner didn't follow the case or Conlon's campaign for justice in detail.
"It didn't seem a big deal back then," he said.
"I was in Long Kesh with dozens of guys who were innocent, guys who had statements beaten out of them by the police.
"It was a common occurrence."
O'Rawe's book details Conlon's crazy troubled life after he was released from prison in 1989.
Over the next decade, Conlon would go on to blow the £1m that he received in compensation and from book royalties and film rights.
He gave money away, taking in "all sorts of waifs and strays, buying them food and clothes and whatever they needed", his friend says.
"Gerry couldn't walk past a beggar," he says.
"He wouldn't just give him money.
"He'd kneel down to talk. 'Tell me your story', he'd say."
The rest was spent on drugs, drink and women.
"It was a very different existence to my own as a married man with a family in west Belfast when I got out of jail," O'Rawe says.
Struggling to cope, Conlon became addicted to crack cocaine which he brought home when he returned to Belfast.
"It was just after the IRA ceasefire when the Provos were killing drug dealers using the name Direct Action Against Drugs," he says.
"Gerry was taking it himself, not dealing. But I don't think that would have stopped the IRA targeting him had he not been so well known."
Conlon tried to kick his addiction many times and eventually succeeded in 1998.
The book covers his often violent relationship with fellow addict Angie, who once put a razor blade in his shoe to cut off his toe after they argued.
He was also well known to London prostitutes.
"His flat was like Piccadilly Circus with call girls coming and going," O'Rawe says.
"But he wouldn't have sex with them, he didn't need to pay women for that, he just wanted to talk."
Shortly after he was freed, he slept with a Dublin journalist.
"They were having a smoke after going to bed and Gerry said to her 'You're number 155'," says O'Rawe.
"He was so immature.
"You don't grow up in jail.
"Inside, he was still 20."
In 2008, Conlon was contacted by a nurse named Linda whom he had a relationship with in 1989.
She told him that she had got pregnant and he had a daughter who was a law student at Queen's University.
"Linda was very good for Gerry," says O'Rawe.
"They didn't live together, but she settled him down," says O'Rawe.
Conlon died of lung cancer in 2014.
Before he passed away, he asked his best friend to write a book telling his story.
"When he was in hospital, he sent for two people - his solicitor Gareth Peirce and myself," O'Rawe says.
"He asked me to bring him down a fry.
"We ate our sausage sodas together in the hospital room. 'I'm tired, Richard', he told me.
"Then as I was going out the door he said, 'I love you'
"He'd never said that before.
"I told him that I loved him too.
"I still miss him so much.
"There's nothing stronger than a childhood friendship.
"When we were together, even as middle-aged men, there was an electricity.
"It was like we were back in Peel Street listening to Radio Caroline on the transistor at the street corner."