Cher’s son Chaz Bono says he feels complete for the first time in his life since having gender reassignment surgery.

The 41-year-old has now completed transition, having had surgery in 2009. He legally changed his name last year.

A documentary on his transformation, Becoming Chaz, was shown at the Sundance Film Festival in Utah on Sunday.

Bono has kept the details of his transition under wraps until now, but the film shows him preparing for breast removal surgery and the effect his decision has on his relationship with his girlfriend of five years, Jennifer Ella.

Speaking in the film, he said: “It’s the greatest thing I’ve ever done in my life. It’s the only time I’ve felt like a complete person.”

He added: “I’ve hated my body since puberty.

“When I was a little girl, I would go to sleep at night praying I’d wake up as a boy. I just knew I wanted to be a boy.”

The film also shows Cher’s reaction to the surgery. The star admitted she was “terrified” about her child having the surgery but concluded: “You’ve got to do what your heart tells you to do.”

Bono added that he wanted to make the documentary to change attitudes to transgender people.

He said: “I wanted to do this because I wanted to help people. And I knew that I could put a face on this issue that people just don’t understand because it’s a hard one to understand. I wanted to be able to change people’s hearts and minds on this.”