The disgraced basketball player was caught on camera kissing an unidentified woman in a nightclub just days before his girlfriend gave birth to their daughter True last month, while video of another woman joining him at his home last year, when Khloe was three months pregnant, also surfaced.
Just hours after Kim addressed Tristan's behaviour during an interview on The Ellen DeGeneres Show which aired on Monday, she made the decision to publicly unfollow him on Instagram - with him then returning the favour.
Speaking to host Ellen, Kim took a deep breath before speaking about the situation, telling her: "I just don't know how to describe it, besides it's just so ****ed up!
"We really were rooting for Khloe... and she's really doing the best that she can; it's a really sad situation all over," Kim added, before telling Ellen she has vowed not to bad mouth any of her siblings' exes, especially if there's a kid involved.
"I kinda made this rule with my brother (Rob Kardashian): If there's a baby involved... I'm gonna, like, keep it classy, and not talk too bad," she explained. "One day True is going to see this and, you know, it's so messed up."
Khloe has not publicly commented on the infidelity claims, and has been relatively silent on social media since the birth of baby True. However, reports have suggested Thompson, who was at Khloe's bedside when she gave birth, is doing his utmost to save his relationship with the reality TV star.