Adam’s home is a rented ramshackle cottage in a rundown suburb of LA – with a garden full of weeds.
With his partner Charity, he struggles to make ends meet and their only child, ten-year-old Normandie, is being cared for by Leonardo’s father George and Adam’s mother, Peggy, after she was removed from Adam’s care in 2014.
Now, at the age of 45, he has decided to break a lifelong vow of silence to tell The Mail on Sunday how his superstar sibling’s fame, the drugs and the temptation that came with his celebrity lifestyle, tore their relationship apart.
‘Leo wants to save the world but he seems more concerned about the environment and climate change than he does about his own brother. It hurts,’ he laments.
‘We were once so close,’ says Adam, shaking his head sadly. ‘I loved him and I still do. But we’ve not spoken in a couple of years. The last time I saw Leo was at his birthday party a couple of years ago.
‘I’d been invited by another friend. Leo was pleased to see me and gave me a hug. But when I try to call him, my messages go unanswered. He has a whole team around him now and it’s impossible to penetrate that wall of hangers-on.’
It is not entirely surprising to learn that his famous brother has distanced himself. Adam’s face and slight body are gaunt from years of drug abuse, although it is an addiction he now swears he has kicked.
Although they grew up side by side, they are not genetically related: Leo’s father George split from his German mother Irmelin when DiCaprio was just a year old to create a new family with Adam’s mother, Peggy. Even so, says Adam, the two boys ‘had a bond that was thicker than blood’.
I ask Adam if he blames his brother’s success for his subsequent decline into addiction, but the answer is no.
‘It was a heady world and I embraced it. I’m a grown man and I’m responsible for my own actions. I don’t blame Leo for that.’
Adam toured extensively as part of his brother’s entourage and still treasures the ‘appreciation gift’ Leo gave him for his loyalty – a stainless steel Rolex which Leonardo received for Titanic.
‘By the late 1990s I was living with Leo in a rented home above Sunset Str!p, with another actor friend. We’d party all night and sit around smoking pot and playing video games, though Leo never smoked pot. He hated the smell.’
By 2008, Adam’s marijuana and cocaine habit had turned into a serious heroin addiction and his brother began to keep his distance.
‘I was arrested five or six times for petty theft, shoplifting from supermarkets, trying to support an opiate addiction of half a gram to a gram a day,’ explains Adam.
‘Leo and I never had an argument. But he started surrounding himself with people that didn’t want me around. He’s the biggest star in the world and there’s me, messed up on drugs. I was slowly shut out of his world.
‘Finally I got tired of going in and out of jail. I’ve been off heroin since 2013
Adam says he is speaking out now in an attempt to reach out to his brother and repair their severed relationship – and because he is desperate to see his daughter.
‘I admit to making mistakes but Charity and I have not seen our daughter in two years. All we want is for Normandie to know her parents. In this town, the DiCaprio name and money counts for a lot. My mother used Leo’s name in court and I am sure that influenced the judge. I don’t want anything from my brother but I’m the only brother he has. I just want him in my life. And I want to see my daughter.’
Indeed, far from envying his brother’s riches and success, Adam says he pities him.
‘I see his life now, the fact that he’s still doing the partying and hanging out with models, and I feel sorry for him. He hasn’t grown up.
‘I’ve been with the same woman for 17 years and have a kid, but Leo’s still a playboy.
‘When he first got famous he told me how lonely it felt. How he didn’t know who he could trust. I think that’s part of why he is like he is now. He’s seeking something to make his life complete. I hope for his sake he finds it.’