bieber040311_01_X17230WM.jpgJustin Bieber has fathered a son with a 20-year-old California woman, according to Star magazine.

Mariah Yeater claims she and Bieber had sex following his concert at the Staples Center on October 25th of last year. As a result of their encounter, Yeater claims Tristyn Anthony Markhouse Yeater was born.

In a California courtroom under oath, Yeater told 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."

A rep for Justin Bieber has denied the claims. The following statement was issued:

    "While we haven't yet seen the lawsuit, it's sad that someone would fabricate malicious, defamatory, and demonstrably false claims. We will vigorously pursue all available legal remedies to defend and protect Justin against these allegations."

Bieber Tweeted the following:

"so Im going to ignore the rumors...and focus on what is real. an opportunity to help by doing what i love. Judge me on the music! Love yall!"

Yeater is asking the courts to have the 17-year-old pop star take a paternity test to prove he's the father of the little boy. She's also asking for financial support.

A hearing has been scheduled for December.