By Dylan Howard - Senior Executive Editor, Star magazine and David Perel - Editor In Chief, Star magazine

Teen pop icon Justin Bieber got a 20-year-old Californian woman pregnant during a backstage tryst and admitted it was his "first time," she claims in a sensational lawsuit obtained exclusively by Star magazine.

Mariah Yeater filed court papers saying that her sexual encounter with the "Baby" hit-maker occurred on October 25 of last year, after he performed to a sold-out crowd at L.A.'s Staples Center.

20-Year-Old Woman Claims Justin Bieber Is Father Of Her Baby, Files Paternity Lawsuit

As Breaking Celebrity News previously reported, the woman has filed a bombshell paternity suit against Bieber, alleging he is the father of her three-month-old baby.

In a hand-signed affidavit, sworn under the penalty of perjury, Yeater wrote that  a security guard working for Bieber approached her and "asked if I wanted to meet Justin Bieber" before whisking her backstage.