Just one day after Breaking Celebrity News broke Kourtney Kardashian was caught flirting with Khloe's ex French Montana at P. Diddy's birthday party, a source now reveals exclusively to Breaking Celebrity News the new mom has "lost it!"

The reality star allegedly went nuclear on Kourtney after she was caught "twerking" with French at Sunday's star-studded bash.

"Khloe went in, telling Kourtney she was out of line, disrespectful, and desperate," a source close to Khloe told Breaking Celebrity News. "Khloe was beyond hurt. She felt utterly betrayed and was ashamed of Kourt and couldn't stop screaming.

Now the sisters "aren't speaking," said the informant. "Khloe’s going through a lot of s**t in her life and feels Kourt should have known better and have more respect for her and not be hit on her exes."

As Breaking Celebrity News previously reported, Kourtney and French were quite the item at Diddy's shindig . A source who attended the party told Breaking Celebrity News exclusively there was serious flirtation between the rapper and the mother-of-three.