Sir Mo Farah has revealed that he was illegally trafficked into the UK under the name of another child.
The four-time Olympic champion long-distance runner said "the truth is I'm not who you think I am," adding that he needed to tell his real story "whatever the cost" in the BBC documentary The Real Mo Farah.
"Most people know me as Mo Farah but it's not my name or it's not the reality," said the father of four, 39.
"The real story is I was born in Somaliland, north of Somalia, as Hussein Abdi Kahin. Despite what I've said in the past, my parents never lived in the UK.
"When I was 4 my dad was killed in the civil war. You know as a family, we were torn apart.
"I was separated from my mother, and I was brought into the UK illegally under the name of another child called Mohamed Farah."
"Family means everything to me and you know, as a parent, you always teach your kids to be honest.
"But I feel like I've always had that private thing where I could never be me and tell what's really happened.
"I've been keeping it for so long, its been difficult because you don't want to face it, and often my kids ask questions, 'Dad, how come this?'
"And you've always got an answer for everything, but you haven't got an answer for that.
"That's the main reason in telling my story because I want to feel normal and … don't feel like you're holding on to something."
Sir Mo's wife Tania Nell said in the year leading up to their 2010 wedding that she realised "there was lots of missing pieces to his story", but she eventually "wore him down with the questioning" and he told the truth.
During the documentary, Sir Mo said he thought he was going to Europe to live with relatives and recalled going through a UK passport check under the guise of Mohamed at the age of 9.
"I had all the contact details for my relative and once we got to her house, the lady took it off me and right in front of me ripped them up and put it in the bin, and at that moment I knew I was in trouble," he said.
The athlete travelled back to his childhood home in Hounslow recalling "not great memories" where he was not treated as part of the family.
"If I wanted food in my mouth my job was to look after those kids, shower them, cook for them, clean for them, and she said, 'If you ever want to see your family again, don't say anything. If you say anything, they will take you away.'
"So she told you don't talk about anything, otherwise I was in big trouble and I guess for me the only things that I could do, in my control was to run away from this was get out and run," he said.
Sir Mo eventually told his PE teacher Alan Watkinson the truth and moved to live with his friend's mum, Kinsi, who "really took great care" of him and he ended up staying for seven years.
It was Mr Watkinson who applied for Sir Mo's British citizenship, which he described as a "long process", and on July 25, 2000, Sir Mo was recognised as a British citizen.
Sir Mo, who named his son Hussein after his real identity, said: "I often think about the other Mohamed Farah, the boy whose place I took on that plane and I really hope he's OK.
"Wherever he is, I carry his name and that could cause problems now for me and my family.
"The important thing is for me to just be able to look and say this is what's happened, and just being honest, really."
In the documentary, a barrister tells Sir Mo that although he was trafficked into the country as a small child and he told the relevant authorities the truth, there is still a "real risk" his British nationality could be taken away as it was obtained by misrepresentations.
But it is understood the Home Office will not take any action against Sir Mo and he will not be deprived of his citizenship.
The department's guidance makes clear that it assumes a child is not complicit in gaining citizenship by deception.
"If the person was a child at the time the fraud, false representation or concealment of material fact was perpetrated [that led to citizenship], the caseworker should assume that they were not complicit in any deception by their parent or guardian," the guidance says.
"I don't think I was ever ready to say anything — not because you want to lie, but because you're protecting yourself," said Sir Mo, speaking to his wife.
"I Think you only realise later on down the line its OK to let things out and say how it happened.
"But in this, I think you know I was trafficked and that's what it feels like."
The documentary ends with Sir Mo speaking to the real Mohamed Farah before saying he will continue to go by the name he was given when he entered the UK.
The Real Mo Farah will air at 6am on BBC iPlayer and 9pm on BBC One on July 13.