The 30-year-old Boston Celtics player went through his lawyer Marty Singer, who called his alleged hookup Sydney Chase a "liar" and claimed she had zero proof to back up her cheating allegations.
Tristan's attorney reportedly fired off a cease and desist letter to the 23-year-old model, making it clear the NBA star denies the two ever had an affair.
Calling her allegations "malicious defamatory fabrications," Singer stated, "Mr. Thompson had no relationship with you whatsoever and he never sent you any such texts."
He continued by claiming Sydney can't prove anything because nothing between the two happened.
"It is obvious that you are a liar," the letter reportedly stated. Ending the fiery legal letter, Tristan's attorney warned the model that if she didn't quit talking about his client, Khloé Kardashian's baby daddy is going to sue.
Insinuating that she's speaking to the media, Singer wrote, "you do so at your peril since you may find yourself in court attempting to defend your indefensible misconduct."
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According to Sydney, they met in November but hooked up earlier this year while he was dating Khloé. The model says that Tristan told her he was single and his baby mama wasn't "his type."
Sydney also alleges that Tristan reached out to her on April 13 -- the day after his daughter with Khloé's birthday -- when he was in Boston.
This is the first time we've heard Tristan's side of the story but that didn't stop Khloé from allegedly sliding into Sydney's DMs.
The KUWTK star made eyebrows raise when she shared the latest promo showing her FaceTiming Tristan from Boston, where some of the alleged flirty conversations with Sydney took place.