London Mayor Boris Johnson has admitted that he would like to be prime minister but insisted "it's not going to happen".
The politician, 48, who has been seen as a possible future rival to David Cameron, said he would want to "have a crack" at the job "if the ball came loose from the back of a scrum".
He was asked whether he harboured ambitions for the top job in British politics in a forthcoming BBC2 documentary.
Michael Cockerell, who made the programme, told the Radio Times that Mr Johnson answered: "I would like to be the lead singer of an international rock group. That was my aim, or a good guitarist.
"I would love to have been a world-famous painter or a composer. There are many things that I would like to have been able to do."
When the documentary-maker pressed him again, he replied: "I think it's a very tough job being prime minister.
"Obviously, if the ball came loose from the back of a scrum - which it won't - it would be a great, great thing to have a crack at. But it's not going to happen."
Mr Johnson's sister Rachel said that the Mayor, who at the age of 12 painted a self-portrait resembling a Grecian demi-god according to the documentary-maker, set his sights high when he was a child.
"As Boris was growing up whenever anyone asked him what he wanted to be, he would answer: 'World King'," she said.
She said of her brother's current relationship with the Prime Minister, who he went to school with at Eton: "When they're together it's rather sweet, because David Cameron - even though he's taller - looks at Boris as if he's still head boy at Eton.
"Remember, Cameron was two years younger - the young pup."
Asked whether Mr Johnson was now resentful as Mr Cameron had become Prime Minister, she said: "No, it gives Boris a sense of continuing superiority because he was Captain of the School."
Mr Johnson said that he vaguely remembered Mr Cameron at Eton, where the younger pupil was known as "Cameron minor" because his older brother was also at the exclusive school.
"I do remember Dave," he said. "Someone said to me once, 'That's Cameron mi' and there was this tiny chap, I dimly remember."
Mr Johnson said that he felt embarrassed about his past as a member of the notorious Bullingdon Club, a dining group for ex-public schoolboys at Oxford University, whose members also included Mr Cameron.
"This is a truly shameful vignette of almost superhuman undergraduate arrogance, toffishness and twittishness," he said.
"But at the time you felt it was wonderful to be going round swanking it up. Or was it? Actually I remember the dinners being incredibly drunken."
Asked about the club's reputation for smashing up restaurants, he admitted: "Yes. And the abiding memory is of deep, deep self-loathing."
Mr Johnson found that he could make people laugh at school.
He admitted: "As a general tactic in life, it is often useful to give the slight impression that you are deliberately pretending not to know what's going on - because the reality may be that you don't know what's going on, but people won't be able to tell the difference."