Send your Letters of Support to Chaz!

Tonight on ET in a world exclusive interview, Chaz Bono talks with Mary Hart for the first time about his stunning transition from Chastity to Chaz!

"[The most difficult step was] finding the courage not to worry about what people would think of me so much," Chaz tells Mary. "I always felt like a male from the time I was a child."

Once thought of as Sonny and Cher's adorable little daughter who captured the hearts of television audiences, Chaz is now 40 and a lifetime away from that little girl. Almost 15 years since coming out as gay, he is beginning to live life as he wanted to for a long time - as a man.

"I believe that gender is something between your ears not between your legs," says Chaz, who publicly revealed in June that he was undergoing a gender change. "It was just a long process of being comfortable enough to do something about it. I was turning 40 and I thought it's now or never. I want to still feel vibrant and be able to enjoy my life in a male body and not wait until I am an old man."

Chaz tells ET he had his breasts removed and started taking male hormones in March, which lowers his voice, redistributes fat and promotes muscle growth, hair growth and an increased sex drive, among other things.

"I am literally going through puberty," he says, with negative side effects limited to "just muscle aches… growing pains."

Asked what mom Cher feels about her child's experience, Chaz says he cannot speak for her, however everyone close to him has been nothing but supportive: "The people in my life are just happy that I'm doing this and seeing the positive effect that it's having on me," he says. "[I'm] trying to use my life experience to educate people. … I feel like I'm living in my body for the first time and it feels really good."

Watch ET for more with Chaz Bono.