Mariah Yeater, now 20, seeks to force the popster to undergo paternity testing to prove he's the father of her three-month-old son, Tristyn Anthony Markhouse Yeater.

Yeater contends in a lawsuit filed Oct. 31 that Bieber's security asked her if she wanted to meet the 17-year-old singer, who shortly thereafter took her backstage to a bathroom at L.A.'s Staples Center where the two had "30 seconds" sex. She claims he asked not to use a condom. "He said that because it was his first time he wanted to feel everything."

br>Radar quotes Yeater telling a judge: "On July 6, 2011, I gave birth to a baby boy. That was exactly 36 weeks and two days after the sexual encounter with Justin Bieber. Based upon the timing as well as the fact there were no other possible men that I had sex with that could be the father of this baby, I believe that Justin Bieber is in fact the father of my baby."

Bieber's spokesman Matthew Hiltzik called the claims "malicious, defamatory, and demonstrably false.”

Bieber, who just released a new Christmas album, told Rolling Stone last February that "I don't think you should have sex with anyone unless you love them." On Wednesday he tweeted, "All the rumours . . . the gossip . . . . Im gonna focus on the positives . . . . the music."

When asked during an interview in September how he saw himself in five years, Bieber answered: "By 25 or 26, I want to see myself, like, married or start looking for a family. I want to be a young dad. I want to be able to have done what I wanted to do — to be successful, to do a movie or whatever. But if the time is right, I definitely want to be married by 25."