Chaz Bono, the son of singer Cher, has spoken candidly about his transition from female to male.

Speaking ahead of a book and documentary about his journey, the star said he never had a moment’s doubt that he was supposed to be a man.

Bono, 42, grew up as Chastity and was a lesbian activist for many years. He announced two years ago that he was transitioning and completed the process last year, albeit in the public eye.

Speaking to TIME, he said he had “confused gender identity with sexual orientation” when younger.

He said: “So when I was about 13 or 14, I realised I was attracted to women and then made the assumption that I was a lesbian, and didn’t realise that that wasn’t the case. It was the fact that I was a man and a heterosexual man. The issue wasn’t my sexual orientation, but rather my gender identity.”

The star, who says he wants to speak up for trans rights, has refused to talk about whether he has had genital surgery.

But he said that he was “thrilled” about the results of his ‘upper’ surgery, or breast removal.

“It was the greatest day, probably of my life,” he said. “It was getting rid of something on my body that felt like it didn’t belong there since they started to develop at, like, 11 or 12.”

Bono revealed that he spent time talking to psychologists about how he would deal with transition but said he “never had a moment’s doubt” about whether it was the right thing to do.

He said: “I had felt uncomfortable as a women my whole life. So that wasn’t the issue. It was about finding the strength to transition and how that would affect my life.”

The star added that he was continuing to publicise his journey to “bring awareness” of the issue.

Becoming Chaz will be broadcast in the US on the Oprah Winfrey Network tomorrow.

Bono’s memoirs, Transition: The Story of How I Became a Man, will also be released this week.