Rihanna and another singing star got into a catfight this weekend when a comment Ciara made on TV soon escalated into a Twitter feud, according to Us.

As a 'Fashion Police' guest on E!, Ciara, 25, opened up about the redheaded pop sensation:

"I ran into her recently at a party," the singer said of Rihanna. "She wasn't the nicest....It's crazy, because I've always loved and respected what she's done in fashion. It wasn't the most pleasant run-in."

In response, 'Fashion Police' co-host Joan Rivers -- never one to mince words (just ask Jennifer Aniston) -- simply sniped, "B--ch."

Rihanna, 22, didn't take kindly to the televised slight, and decided to tweet: "My bad Ci, did I forget to tip you? How rude of me....You gangsta huh? Ha."

And the snark didn't stop there.