Khloé Kardashian's Ex Tristan Thompson Files Libel Lawsuit Against Paternity Accuser

Tristan Thompson has taken legal action against a woman claiming that he is the father of her child.

According to documents obtained by PEOPLE, the NBA star filed a libel lawsuit against paternity accuser Kimberly Alexander. The complaint comes after Thompson, 29, and his ex Khoé Kardashian, 35, sent a cease and desist letter last week demanding the woman "immediately stop defaming them with malicious defamatory lies and specious fabrications," according to reports.

In the lawsuit filed Monday, the couple's lawyer Marty Singer alleges that Alexander is a "wannabe social media influencer and pornographic model/performer who is so desperate to achieve her fifteen minutes of fame that she recently fabricated a false claim that NBA star/Cleveland Cavaliers center/power forward Thompson is the father of her nearly five year old son."

Singer reportedly writes, "Alexander has persisted in publicly proclaiming that Thompson is her child's father and she has maliciously accused Thompson of being a deadbeat dad, ‘neglecting' and failing to take financial responsibility for the child since birth. Such statements are absolutely false and are defamatory per se. To quote Michael Jackson, 'the kid is not [his] son.'"

Additionally, the complaint states that the paternity test Thompson took in January "definitively concluded that [he] is not the father." Thompson also reportedly offered to take a second test, provided they use another reputable third party facility.

PEOPLE has reached out to Alexander for comment. Last week, asked for her response to the cease and desist, she told PEOPLE, "I feel like the whole issue originally stemmed from Tristan not wanting to choose a neutral setting for the DNA testing. Also using a Kardashian associated DNA testing facility. I feel as if you really have nothing to hide then why not just go to a neutral testing site. And also we both know what happened and exactly what went on between us. That's all I can say for now. Thank you again for reaching out."

Thompson shares 2-year-old daughter True with Kardashian, and 3-year-old son Prince with ex Jordan Craig.

While Thompson and Kardashian called it quits last year after two separate cheating scandals, they have remained on good terms and have discussed the possibility of having a second child together.

A source recently told PEOPLE that Thompson has been transparent with Kardashian about the current situation with Alexander, and immediately informed her when she requested that he take a paternity test.

"Tristan has been open with Khloé from the beginning when it comes to the paternity test," said the source. "He told her that he needed to take the test, but also that he didn't believe that he is the dad."

"Khloé and Tristan have both worked hard to get to the point where they are now," continued the source. "Regardless of the issues that Khloé has had with Tristan, he has always been a responsible and great dad. Khloé will continue to support Tristan."

According to the source, they spent Mother's Day together as a family earlier this month.

"They are amazing co-parents and are able to give True a great upbringing together," said the source.