"I think we stayed up until about 3:00 in the morning and laughed and talked," his mother, Leila Lambert recalled. "I didn't want to pressure him. I knew for a long time and I just assumed. ... I knew this is who he is, who he was, and. ... I felt comfortable with it."
Lambert excelled on stage, performing in countless musical theater performances throughout his teens and early career.
Since graduating from high school in 2000, Lambert has lived an openly gay lifestyle in Los Angeles -- dating, and stumbling through relationships like everyone else. He's currently dating, but won't mention any names.
"I've had my heart broken. I've chased after people and had it not work out," he said. Throughout my entire 20s, I've wanted to be in love. That's what I want. I think everybody deserves that. And I've only been in love once. So I'm still looking."
During "American Idol," all eyes were on Lambert, who landed the coveted endorsement of the fussy judge Simon Cowell for his rendition of "Mad World." (His cover of "Mad World" is currently at No. 44 on Billboard's Hot 100.)
Lambert told "20/20" he sought to distinguish himself from the other contestants throughout the competition.
"I just wanted to stand apart from everybody else. I always have to be different," he said. "I wanted to pick songs that I believed in. That was part of my strategy. ... If all the other contestants were singing up-tempo songs that week, I would pick a ballad. If they were all singing ballads, I would pick an up-tempo."
In the May finale, with nearly 100 million votes cast for the two contestants, 23-year-old Kris Allen beat out Lambert for the title.
Lambert said he wasn't "robbed."
"I think being a sore loser just sucks. I think that's tacky," he said. "We're two very different types of artists, and I don't see how people can say one is better. I love listening to Kris sing and watch him play. And I think that he enjoys watching me do my thing."
In fact, Lambert admits to thinking his competitor, Allen, is hot.
"He's a good-looking guy," he said. "I think that a lot of people out there who watch the show can agree with me."
Despite his runner-up status, the future looks bright for Lambert, who landed a contract with 19 Recordings -- the production company owned by "American Idol" creator Simon Fuller -- and announced plans to release a debut album this fall on RCA Records.
"It's surreal," he said. "It's really, like, everything that I ever wanted is happening and ... I don't know how to react. I'm thankful. I am proud."
With a busy schedule ahead, Lambert said he has to stop himself from whining about the daily grind and remember the bigger picture.
"Every time I am tempted to complain about it, or I start getting a little bit like, 'Ugh,' I just rewind about a year and a half ago when I was ... sitting on my a** and not satisfied."
"I get to be that rock star that every kid fantasizes about being," he said. "I get to sing and entertain and make people happy and ... hopefully forget about some of their problems, or make them feel better about some of their problems -- just take them for a ride," he said. "That's the coolest job in the world."
Lambert is not concerned that his sexuality will deter fans or limit his future career options.
"I don't think it's going to limit anything," he said. "I can see how certain people might get turned off by it. And if they do, it's their loss, you know?"