"I am gay, and I'm very comfortable with it," 27-year-old Lambert revealed.
Watch Adam Lambert's interview on "20/20" Friday at 10 p.m. ET.
"'Come out' is so funny to me because I've never been in," the former "Idol" contestant told ABC News. "I've always been out. I just chose to avoid it. I didn't ... I don't feel closeted. Everybody that I worked with knew about my personal life."
When asked by "20/20" why the season-long favorite decided not to publicly acknowledge his sexuality until after the show, Lambert said that he didn't want being gay to upstage him.
"I wanted the focus to be on my ability as a singer and as an entertainer -- not on my private life," he said. "So I chose to kind of ignore the issue until after the voting ended."
The flamboyant singer also dispelled any rumors that "American Idol" producers asked him not to address his sexuality during the show.
"They were 100 percent supportive the entire time," he said. "They asked me, 'What do you want to do? Would you like to talk about it? No? Fine.' They respected it either way. They respected my choice."
While Lambert now proudly talks about being gay, he said he's also openly exploring his sexuality.
"I've been kind of toying around with the bi thing in my head. I wouldn't ever give myself the label 'bisexual,' but bi-curious? Yeah," he said. "I've been known to make out with girls from time to time. Couple drinks involved, you know. It's fun. And who knows? Maybe it'll go further someday. I don't know."
Experimentation and boldness are familiar to Lambert. Photos surfaced online of the pop star dressing in drag and kissing another man, which Lambert confirmed were real.
As for the throngs of adoring, young, female fans, many of whom harbor fantasies about the "Idol" star, Lambert said he is flattered.
"I have crushes on women all the time," Lambert said. "I don't have intimate relationships with them, but I find women beautiful. ... I think femininity is a beautiful, beautiful thing. And to be the object of desire to a woman is a great compliment."
Growing up, the San Diego native loved musical theater, dancing, playing dress up and was obsessed with glitter -- all interests that Lambert said highlighted his sexual preference from a young age.
Instead of the stereotypical "coming out" ritual homosexual teens have with parents, Lambert said his mother actually "outed" him, asking him on a car ride home if he wanted a girlfriend or a boyfriend.
"It was very subtle. ... That was the cool thing, is that without actually saying it, I was myself," he said. "I always felt support. And I was always able to be creative at home. And there was no taboo."