Over the years we've seen the ladies of the Kardashian clan fight over just about everything.
But the sisters have always observed an unwritten code of honor when it came to keeping their distance from one another's former loves.
Now, however, Kourtney Kardashian, seems to have tossed those rules out the window.
According to a new report from Radar Online, Kourtney was spotted getting intimate with rapper French Montana in a club earlier this week.
French dated Khloe Kardashian in 2014, and the relationship was so serious there were credible reports of the couple getting engaged.
“Kourtney and French were on each other,” an onlooker at West Hollywood club Ysabel tells Radar Online.
“She was twerking on him, he had his hand on her waist and ass and was whispering in her ear all night.”
The source says Kourtney did nothing to deter French's advances.
“She was eating it up,” the witness claims.
“She was smiling in his face and was hand feeding him hors-d'oeuvres.”
Another insider says French and Kourtney were “too close for comfort” and were “looking like they wanted to do some X-rated things.”
Shockingly, the flirtation reportedly occurred at Diddy's birthday party on Sunday night, the very same night that Keeping Up With the Kardashians depicted the aftermath of Tristan Thompson cheating on Khloe while she was pregnant with his child/
“You may forgive but forgetting is not possible," Khloe tweeted during the episode.
"Looking back that I was in shock because I couldn’t believe that this would ever happen to me but I’m still very proud of myself for how I handled everything.
"True gave me the peace and strength I needed.”
If the reports about Kourtney and French are true, then it's possible that Kourtney was being betrayed while she tweeted about a previous betrayal.
As for Kourtney, she's reportedly dating Luka Sabbat, but sources say the relationship is not serious or exclusive.
There's no word yet on Khloe's reaction to the news that her sister was spotted hooking up with her ex.
But we're gonna go out on a limb and assume she's not crazy about the situation.
It's also a safe bet that the cameras will be rolling when Khloe confronts Kourtney about this mess.