The 29-year-old former "American Idol" runner-up, multiplatinum recording artist and Broadway star credits his son, conceived by in-vitro fertilization with friend and producer Jaymes Foster, with making him realize that he could no longer hide his homosexuality from the world.
"It was the first decision I made as a father," Aiken told the magazine, which arrives on newsstands Friday. "I cannot raise a child to lie or to hide things. I wasn't raised that way, and I'm not going to raise a child to do that."
Aiken, who rose to fame on "Idol" in 2003, has long been subject of rumors and tabloid fodder that he was gay, but usually refused to acknowledge them. In an interview with The Associated Press two years ago, he said of the talk: "I don't really feel like I have anybody to answer to but myself and God and the people I love."
Aiken said he only told his family that he was gay four years ago. He recalled a tearful discussion with his mother in a car after dropping off his brother, who was being sent to Iraq, at a military base.
"It was dark. I was sitting there, thinking to myself. I don't know why I started thinking about it ... I just started bawling. She made me pull over the car and it just came out," he said. "She started crying. She was obviously somewhat stunned. But she was very supportive and very comforting."
Aiken said his mother "still struggles with things quite a bit, but she's come a long way."
The magazine cover features Aiken holding his son, born in August. Aiken, who considers himself a born-again Christian, said he knows he may turn off some fans - known as Claymates - with his admission and his decision to have a child outside traditional marriage.
"I've never intended to lie to anybody at all," he said. "But if they leave, I don't want them to leave hating me."
Gay groups applauded Aiken's public admission.
"We congratulate Clay for making this decision and for setting an example for others and his family," said Neil Giuliano, president of the Gay & Lesbian Alliance Against Defamation. As we're seeing, more and more gay people, including celebrities, are living openly and honestly, and this has tremendous impact in terms of creating awareness, understanding and acceptance."
Aiken recently released the CD "On My Way Here" and made his Broadway debut this spring in "Monty Python's Spamalot."