They were once as close as two brothers could be - two young boys from Los Angeles taking their first, tentative steps in the film business.
One of them, Leonardo DiCaprio, is now an Oscar-winner who commands NZ $35 million per movie, having starred in hits such as Titanic, The Revenant and The Wolf Of Wall Street.
He is also famous as a do-gooder - one who, earlier this year, flew his Los Angeles friends 6,000 miles to St Tropez to raise money for his global warming charity.
For Adam Farrar, though - the older step-brother who inspired DiCaprio to act - life is rather different: today he leads a hand-to-mouth existence as a struggling TV scene-painter on the poorly paid fringes of the show business world, the Daily Mail reports.
DiCaprio, 42, has a vast property empire including a $26 million Beverly Hills mansion, an $14 million Malibu beach pad and a £21 million New York penthouse, not to mention his own palm-fringed private 104-acre island off Belize.
Adam's home is a rented ramshackle cottage in a rundown suburb of LA - with a garden full of weeds.
'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.
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 are talking as he sips iced tea outside Palermo, an Italian bistro just a stone's throw from the modest red clapboard home where he and DiCaprio grew up.
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'.
Adam lived with George and his mother Peggy, a devout Amritdhari Sikh who has become something of a fixture at Hollywood functions thanks to her trademark turban and flowing robes.
Leo, meanwhile, divided his time between George and Irmelin, who moved into a small home two streets away.
'I loved having a little brother, and we got along really well,' Adam recalls. 'Leo was very light blonde when he was young, and he used to get mistaken for a girl, though his hair grew darker with age. He was always a good-looking kid.'
He recalls the usual childish tantrums: 'A couple of times Leo tried to run away from home after arguments. I remember him as a six-year-old packing his clothes in a suitcase and marching off down Hollywood Boulevard. I wanted to run after him but his mum said, "No, no. If he wants to run away, let him." He eventually came home.
'We'd go to the beach in the summer and skiing in winter. Our parents took us to the natural history and science museums. As we grew older we'd play video games together, ride our BMX bikes, and played handball for hours against a parking lot wall.
'I took violin lessons, and Leo took piano. We both loved breakdancing, and were pretty good at it. If a crowd formed outside Palermo, we'd put out a hat and breakdance for cash. We did pretty well.'
DiCaprio has made much of his tough childhood on the streets of Los Feliz.
Today, it is a trendy suburb of Los Angeles, but back in the 1970s it was blighted by drug dealers and gangland warfare.
Theirs was a safe, if bohemian home. Leo's father George was a comic book designer and firmly part of the counter-culture movement of the 1960s. It speaks volumes that his best friend was psychologist, writer and LSD 'guru' Timothy Leary.
George split from Leo's German-born mother Irmelin when Leo was just a year old and it was not long before he started a new relationship with Adam's mother Peggy.
'Leo would often stay at his mother's home, just a block away, and I'd stay with him,' says Adam. 'We were as close as any two brothers could be.'
But growing up in Los Feliz in the 1970s, meanwhile, could be wild.
'Leo and I would see people smoking marijuana and snorting cocaine. I think that exposure left Leo with an aversion to drugs. It bothers him if anyone lights up a joint around him.'
Close as they might have been, it seems there is a lingering sense of unfairness about the past - even as children, Adam felt the two were not always treated equally.
'Leo was George's son, and he naturally showed more affection to Leo,' he says.
'At Christmas, Leo would have a big pile of toys, and I'd have just a couple of gifts in the corner. Leo was sent to private school, while I went to the local state school. Our parents gave us love but I felt Leo was favoured.'
It was actually Adam who led the way into show business, starting at the age of six.
He was asked to audition for a commercial and a string of adverts, and minor TV roles in shows like Eight Is Enough and Battlestar Galactica followed: 'Leo saw what I was doing and that's what got him interested in acting.
He hated school and when he saw I was making good money and you could be schooled on set, he asked if he could do it too.
'Leo started acting when he was about nine or ten, starting with a Matchbox toy car commercial, which led to other jobs, and though he wasn't an overnight success, he stuck with it, because the alternative was homework. As a child actor he only had to study a couple of hours a day on set.'
It was not long before Adam was eclipsed. Leo landed a role on the American television series Growing Pains then, at 16, was picked by Robert De Niro for This Boy's Life, which led to a series of critically-acclaimed independent films.
The real breakthrough, however, came with Titanic in 1997, which took $2.5 billion at the box office and turned DiCaprio into a worldwide sensation.
Not that he was expecting it, says Adam: 'Leo was actually convinced he'd made a terrible mistake with Titanic. He was convinced it was going to be a flop. Then he became the biggest star in the world.'
As DiCaprio's star soared, his brother became his de facto bodyguard, best friend, and 'party buddy' while running his growing fanclub from the family garage.
Adam was a central character in DiCaprio's group of friends, which included Spider-Man star Tobey Maguire, Ben Affleck and Mark Wahlberg, who would later write and produce the hit TV show Entourage based on the posse's wild bachelor days.
DiCaprio dated a string of supermodels including Giselle Bundchen, yet wisely shunned drugs; his brother, in contrast, became engulfed by endless parties with their offers of 'free women and free cocaine'.
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.
There were penthouse suites in Paris while DiCaprio filmed The Man In The Iron Mask, endless freebies ('designers would send handfuls of clothing, Prada, Gucci, Armani, you name it') and, of course, the endless drugs.
'We went with Demi Moore to Versace's last show in Paris before he was killed and Gianni fitted us both for suits himself. After the show we partied with all the Victoria's Secrets models. We'd go to the Playboy Mansion and hang out with Oliver Stone.
'One New Year's Eve, Planet Hollywood loaned us their private jet to fly to Miami for a week, and then to New York, where we took an entire floor of rooms at the Mercer Hotel. We'd fly to championship basketball games, and hang in the locker rooms.
'By the late 1990s I was living with Leo in a rented home above Sunset Strip, 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.'
But he hasn't entirely avoided brushes with the law. Adam was jailed in Texas for ten days in 2014 thanks to an outstanding warrant in Los Angeles for driving with a suspended licence.
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.
He says while he does not believe DiCaprio was directly involved with him losing custody of Normandie, he thinks the famous name swayed the judge in the case.
'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.'