Mark Lester says he is convinced he is Paris Jackson's real dad.
The former child actor, who played Oliver Twist in 1968 film musical Oliver!, is godfather to Michael Jackson's children Paris, 11, Prince Michael, 12, and Blanket, 7, and is prepared to take a paternity test to prove his claim.
'Michael found it very difficult to have relationships with women.
'I think he'd already tried using his own sperm but it hadn't worked for him, so I made an off-the-cuff comment saying: "Try mine!"'
Mark, who quit acting to become an osteopath, now lives in Cheltenham with second wife Lisa. He has three teenage daughters and a son.
In March 1996, Mark claims Michael took him up on his offer and he attended a London clinic to make the donation.
'Of all Michael Jackson's children I'd assume that the one that looks most like me is Paris,' Mark tells the News Of The World.
'Paris has blue eyes and a pale complexion and high cheekbones. My girls all have very similar features. It's been commented (upon) many times how similar Harriet [daughter Harriet Lester, 15] and Paris are.
'It's been a secret for so long. Michael was a brilliant, brilliant dad. Those kids are Michael's children. He was their father. End of story. But I just want to make sure they're happy.'
A court has awarded Michael Jackson's mother Katherine permanent custody of the children, with closely-monitored visiting rights for Paris and Prince Michael's mother, Michael's ex-wife Debbie Rowe.
The Jackson family have not yet responded to Mark's claims.