Ultimate Betrayal! Kourtney Kaught Flirting & Twerking On Khloe’s Ex French Montana

Khloe Kardashian's ex French Montana was certainly keeping up with the Kardashians over the weekend!

An eyewitness tells RadarOnline.com exclusively the rapper and Kourtney were "all over each other" at P. Diddy's 49th birthday bash on Sunday.

"Kourtney and French were on each other," a source who attended the party at Ysabel in West Hollywood on Sunday, November 4 reveals. "She was twerking on him, he had his hand on her waist and a** and was whispering in her ear all night."

Kourtney didn't mind the attention after her nasty split from boytoy Younes Bendjima. "She was eating it up," said the informant. "She was smiling in his face and was hand feeding him hors d'oeuvres."

The partygoer tells RadarOnline.com the pair appeared "too close for comfort" and were "looking like they wanted to do some X-rated things.”

As RadarOnline.com readers know, Khloe is still suffering heartbreak Tristan Thompson inflicted when he was caught on tape cheating on her with two women.

On Sunday's episode of Keeping Up With The Kardashians, viewers saw Khloe's family react to Thompson's cheating scandal as Khloe live tweeted during the show.

"You may forgive but forgetting is not possible. 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," she tweeted.