Thought the drama on The Real Housewives of New York would end with the exit of former cast members Jill Zarin, Alex McCord, Cindy Barshop and Kelly Bensimon? Think again!

Wetpaint Entertainment has exclusively learned there’s already plenty of discord on the set these days, especially between show veteran Ramona Singer and one of the new girls.

While Bravo has yet to officially confirm the names of the new cast members, it’s been widely reported that they are Jacqueline Kennedy’s relative Carole Radziwill, Yummie Tummie designer Heather Thompson and philanthropist Aviva Drescher.

Now, an insider tells us that one of the three organized a cast trip to London last week — but left Ramona off the itinerary!

“Everyone was invited on the trip except Ramona,” the insider tells Wetpaint Entertainment. “It was a huge diss.”

But while the rest of the cast filmed overseas, fan favorite Ramona exacted her revenge by throwing herself a raucous birthday party at Manhattan’s Bar Italia on November 18.

“She had 24 of her closest friends there and did not seem to miss the other housewives one bit,” a guest at the party tells us.

Best of all? Ramona’s pals surprised her with a pinot grigio-themed cake. “We had it done by Heather Barranco Dreamcakes. It had an edible bottle of Ramona’s label of pinot and edible pieces from her True Faith jewelry line, all made of out hard sugar. The cake looked and tasted great.”

And of course, her guests drank the real version of Ramona’s vino throughout the afternoon.

“Ramona had a blast,” the insider says. “We all did. We spent the afternoon eating, drinking and getting down on the dance floor!”