Kelly Osbourne is not backing down when it comes to her crusade against Christina Aguilera.

A few months ago, Osbourne, 26, called Aguilera, 30, a "fat b****" on E!'s Fashion Police. Over the weekend, Police co-host George Kotsiopoulous defended Aguilera's weight gain, saying she is "still probably a size 2/4" despite her poor outfit choice.

But Osbourne fired back, saying, "Trust me. I'm a 2/4. That is not a 2/4. ... She called me fat for years. I was never that fat."

Aguilera has faced criticism for her weight gain in recent months. Below is a picture of her in September with son Max.