AceShowbiz -

Michael Girgenti insists that Kourtney Kardashian's son Mason is not Scott Disick's, and he apparently has taken legal means to prove his words. According to TMZ, the L.A.-based model who claims he had fling with the 34-year-old socialite in 2009 has filed a paternity lawsuit in L.A. County Superior Court, asking for joint custody.

In the legal docs, Girgenti claims that he met Kourtney during a photo shoot in August 2008. Ever since that encounter, the two allegedly developed texting relationship, which then turned into a sexual one after she and then boyfriend Scott were "on the outs" in March 2009. Saying they "had unprotected vaginal sex," he adds, "I ejaculated inside [Kourtney's] vagina."

Additionally, Girgenti wants the judge to order DNA tests for Kourtney, Scott, Mason and him. A hearing is reportedly set for next month.

In March, Girgenti revealed to In Touch that he believed Mason Disick, who was born 9 months after the alleged sex, was his. "After he was born and I saw photos of him. I began to wonder," the Chicago native said. "I would definitely want to acknowledge Mason if he's my kid. He deserves to know his real father."

A legal rep for the "Keeping Up with the Kardashians" star, however, has slammed the allegations, labeling them "preposterous and an outrageous lie." The rep admitted Kourtney once met him at a photo shoot, but denied she ever gave Michael her contact details.