His name was chanted by crowds at Glastonbury and emblazoned on T-shirts – but Jeremy Corbyn says he was never meant to be called "Jeremy" at all.
The Labour leader said his parents had agreed a name for him shortly after his birth, in 1949 – only for his father to change his mind on the way to having it registered, without telling his mother.
"I was supposed to be called something else," he told comedian John Bishop.
Mr Corbyn said his parents had never revealed their first choice of name.
The MP made the disclosure during TV channel W's John Bishop: In Conversation with Jeremy Corbyn programme, which airs at 21:00 GMT.
He told the comedian: "My mum and dad agreed what I was going to be called and he took the papers to go off and register the birth – and then he changed the name."
Asked if his father, David, made the name-swap without consulting his wife, Mr Corbyn replied: "Yes. To her dying day, she would never tell me what it was.
"I said, 'Can't you tell me what it was going to be?' She said, 'I can't tell you.' So we can only speculate."
The chant "Oh, Jeremy Corbyn" – to the tune of the White Stripes' hit Seven Nation Army – became a bit of an anthem during the Labour leader's appearance at Glastonbury this year, and his supporters chanted "Jez we can" during his leadership campaign rallies.
Describing his family life, Mr Corbyn revealed he felt he had "fallen by the wayside" by going into politics while his three older brothers all became engineers and scientists.
He spoke of his devastation at the death of his geologist brother, Andrew, from a brain haemorrhage while on an expedition to Papua New Guinea, saying that going there to collect his body was "one of the most horrifying and horrific things" he had ever done.
Mr Corbyn also revealed that a neighbour had placed a bet on him to win the Labour leadership at a time when the odds were 200-1.
"Every day I go out on that campaign, he said, 'Are you going to win?'" said Mr Corbyn. "I said, 'I don't know.' He said, 'Look, I've put a lot of money on this – you've got to win.' No pressure, like. I was like, 'I've got to win this for him, now.'"