The traumatic head injury Alex sustained had wiped all of the then-18-year-old's memories, as well as reducing his knowledge of the world around him to that of a small child.
In the months that followed, Alex leant heavily on Marcus, relying on his twin for everything from what a kitchen was for to where they had gone on holidays as children.
But there was just one problem; Marcus wasn't telling the whole truth.
Instead, as new Netflix documentary Tell Me Who I Am reveals, Marcus had concocted a huge lie to hide the truth about their abusive childhood — and the shocking sexual abuse they suffered at the hands of a family member.
After Alex lost his memory at age 18 he relied on Marcus to tell him about their childhood. Photo / Netflix
FILLING IN THE GAPS
Born into a wealthy aristocratic family, Alex returned home to the family mansion in Sussex, England, after his 1982 accident.
Back home, Alex accepted without question the odd behaviours and rules his of his parents — mother Jill and stepfather Jack — as just like any other normal family.
Jill's first husband and twin's father John Lewis had tragically died when they were just three days old in a car accident.
Jack was strict and prone to angry outbursts while their mother was cold and distant, with Alex and Marcus both made to sleep out in a shed outside since they were 14 and forbidden a key to the house.
As Alex had no memory of his friends or family he relied heavily on Marcus to fill him in on the gaps in his life.
Marcus and Alex were made by their parents to sleep in a shed outside and forbidden a key to the house. Photo / Netflix
Alex jokes in the documentary that he "lost my virginity to the same woman twice", his girlfriend at the time.
Marcus told Alex about the details of their childhood, telling him of happy times and beach trips in France when his twin asked if he went on family holidays.
But the truth was the family had never gone on holidays and their parents had been cold and unloving towards them their whole life.
"I painted a picture of a normal family," Marcus said. "But none of that was true. It was a fantasy that I was creating for him."
The happy family facade Marcus had painted for Alex began to fade in 1990 when their father died of pancreatic cancer.
In the days before his death, Jack summoned both his sons to his bed and begged them to forgive him for his behaviour.
The deathbed request puzzled Alex: What was there to forgive?
Even stranger, Marcus flatly refused to accept his father's apology, and he died just days later.
Five years later Jill died of a brain tumour, with Marcus' emotionless reaction setting off alarm bells for Alex, who didn't underside why his twin wasn't upset.
Finally able to access the house they had been denied a key to, the red flags continued, with Marcus and Alex, now 32, discovering fifty pound notes stuffed into jars and sewn into the back of curtains.
When they got to the attic, Marcus and Alex found decades' worth of Christmas presents from relatives and friends meant for them, but had been cruelly hidden away by their parents.
Even more disturbing, a cupboard in a bathroom was stuffed full of sex toys. But the worst find was in their mother's bedroom.
Going through her things, Alex and Marcus discovered a locked cupboard hidden in the back of Jill's wardrobe.
Inside was a naked photo of the twins aged 10, with their heads ripped off — the horrible discovery was too much for either of them to ignore.
Alex demanded to know if their mother had sexually abused them.
"He put his arm around me, and he said 'Yeah it's true' and then we cried. Both of us," Alex recalled.
It was only after their mother died that Alex discovered she had sexually abused him and Marcus as children. Photo / Netflix
COMING TO TERMS WITH IT
Despite coming clean, for decades Marcus refused to tell Alex more about what had happened to them as children, ignoring his brother's pleas to find out more.
Even though there was a Pandora's box existing between them the twins stayed close and each went on to marry and have two children each, as well as running a successful hotel company together.
It was only in emotional scenes shown in Tell me Who I Am, Marcus, now 54, finally revealed the chilling extent of what their mother had done to them; as well as his heartbreaking reasoning for keeping it a secret.
Marcus said his brother's memory loss had been "a gift" — not just for Alex, but also for him as well.
"Alex lost his memory by accident, and I lost my memory voluntarily," Marcus explained. "I was free, I could be rid of all the things she had done to me."
Marcus revealed that not only had they been sexually abused by their mother from the age of 10, but that Jill had also given them to her paedophile friends to be raped and molested.
"She would touch us, she would masturbate us — she would do things that no mother should ever do to our child," he said.
Jill would drive each twin on separate occasions to different friends' houses, stay for dinner and a drink before leaving them overnight to be molested.
"Then in the morning, my mother would come and pick me up and drive me home, never speaking never talking," Marcus said.
The abuse only ended when a 14-year-old Marcus escaped from one man who had tried to rape him and returned home in the middle of the night.
Jill never acknowledged what had happened but the twins were never abused again by their mother or her friends.
Alex and Marcus Lewis want people to know they've gone on to live 'very fulfilled lives'. Photo / Getty Images
'WE'VE ACHIEVED CLOSURE'
Alex and Marcus first went public with their story in a 2013 interview with UK newspaper The Times and a biography that same year, also called Tell Me Who I Am.
However, despite their story attracting significant attention at the time, Marcus refused to tell Alex the details of what had happened to them until they filmed the Netflix documentary.
In an interview with Decider, Alex and Marcus said they had decided to tell their story with Netflix in order to reduce the stigma around childhood abuse.
"We want it to be a conversation that's not taboo," Marcus said. "Maybe you discuss this movie at a dinner party, and a friend tells you, 'You know, I was abused as a kid.'
"I think that would be an amazing thing. People shouldn't be ashamed of what happened in their past, it's not their fault."
Despite the trauma they suffered as children both say they have gone on to live "very fulfilled lives" and continue to be extremely close.
"We've achieved closure beyond anything I could have imagined with each other by making this movie," Alex said. "That's an incredible gift the film has given us."
