Michael Girgenti alleges he had unprotected sex with the reality TV star after they met on a photoshoot in August 2008 and has filed paperwork at Los Angeles County Superior Court in a bid to get joint custody of her three-year-old child, Mason.
Real life drama: Kourtney Kardashian and boyfriend Scott Disick are seen leaving a lawyer's office after it emerged that the reality star is the subject of a lawsuit after a male model alleged HE is the father of her child
Legal bid: Michael has launched a legal bid for a court ordered DNA test in the first steps towards a custody battle over Kourtney and Scott's son Mason
Battle: Kourtney with son Mason who is now at the centre of a lawsuit filed by a man who claims to be his real father
A hearing has been set for next month.
The lawsuit documents the alleged relationship between Kourtney and Michael, which he claims heated up in March 2009, when she told him her relationship with Scott was 'on the outs' and 'she wanted to hang.'
Furious: Kourtney said she was 'furious' when the allegations first emerged, and the model has now filed a claim with the court
However her lawyer told TMZ.com on Friday that Gigenti's allegations are 'absurd'.
'This individual has been selling false and fabricated stories to the tabloids for years about Kourtney Kardashian and her son, Mason. Scott Disick is Mason’s father,' Todd Wilson told the website.
'We have not seen the reported court filing, but we are informed that this individual has been seeking to get paid to publish his ridiculous pleading.
'His claims are absurd and this is simply another shameful attempt to gain publicity and profit from fictional stories about my client.'
Photogenic: Kourtney and Michael met on a photo shoot in 2009, but the star's attorney says there was no further contact after that
Michael claims they had full sex and as soon as she had given birth to Mason - born on 14 December 2009 - he tried contacting her.
The allegations first came to light in March earlier this year when he told In Touch magazine: 'After [Mason] was born, and I saw photos of him, I began to wonder.
'I would definitely want to acknowledge Mason if he's my kid - he deserves to know his real father.'
A legal representative for the Kourtney & Kim Take Miami star previously branded the Chicago native's allegations 'preposterous and an outrageous lie'.
Something on your mind: Kourtney shares an intense conversation with boyfriend on WednesdaySo it must have come as a surprise that the model has now filed papers with the court.
In addition to son Mason, the couple - who have been dating on and off for seven years - have a baby daughter, Penelope Scotland, together.
This is not the first time the extremely wealthy Kardashian family has been confronted by allegations of paternity.
Fashion plate: Kourtney was dressed in head to to black-and-white Chanel
Kourtney's younger sister Khloe, 28, has had to regularly deny rumours that their late father Robert Kardashian was not her biological father.
Their half-sister Kylie Jenner, 15, also recently hit back at reports that Bruce Jenner may not be her real father.
The reality star certainly looked like she had a lot on her mind as she chatted with boyfriend Scott in on Wednesday.
The 34-year-old who looked chic in a monochrome striped dress and espadrilles, certainly seemed preoccupied as she chatted to Scott.
Close: The couple left their young children at home to enjoy some alone timeThe flats bore the distinctive Chanel logo, and co-ordinated well with her chic quilted Chanel bag.
With her hair tied back in a bun and a slick of red lipstick, it was clear Kourtney had made an effort.
Scott however looked far from his usual dapper self in a multi-coloured chequered shirt, blue shorts and leather shoes.
The two left children Mason, three, and one-year-old Penelope at home for their date.
Lots to talk about: With her sister Khloe reportedly having marriage difficulties, big sister Kourtney is sure to be concerned
Just last week it was reported that Kourtney was pregnant with her third child.
She did not comment on the rumours, although was later seen eating sushi with her family - a food type pregnant women are advised to steer clear of due to the raw fish ingredients.
Tea-rific: She protected her perfect lipstick by using a straw as she sipped away on her iced drink
Looking good: She wore a satisfied smile as she got read to clamber into her luxury car