Boxing promoter Frank Maloney has revealed he is undergoing gender reassignment and now lives as a woman called Kellie.
In an interview in the Mirror, Kellie says: "I was born in the wrong body and I have always known I was a woman."
She is working with transgender group TG Pals, whose managing director, Heather Ashton, told the BBC Kellie had been "incredibly brave and courageous".
As Frank, Maloney guided Lennox Lewis to the world heavyweight title in 1993.
In her interview, Kellie says: "I can't keep living in the shadows, that is why I am doing what I am today. Living with the burden any longer would have killed me.
"What was wrong at birth is now being medically corrected. I have a female brain. I knew I was different from the minute I could compare myself to other children.
"I wasn't in the right body. I was jealous of girls."
'Hugely difficult'
Ms Ashton said it had been a "huge decision" for Kellie to come out.
"This is a big deal for any transgender person but particularly for Kellie who's been in the public eye for such a long time.
"This group of people are the last societal group to achieve equality and to be socially accepted."
Ms Ashton said it could be "hugely difficult" for people to tell their partners, families and colleagues, "to come out and say I do love you, this is who I am, and please accept me".
She said she hoped Kellie's example would encourage others contemplating gender reassignment to overcome their fear.
