Kelly Osbourne is at it again picking on Christina Aguilera, this time about her weight gain, claiming she was never as fat as the singer.

On Friday's episode of Fashion Police, Osbourne criticized Aguilera's outfit for the Michael Jackson tribute concert on Oct. 8, which had many people whispering about her weight gain.

She called me fat for years, 26-year-old Osbourne said of Aguilera. I was never that fat.

Joan Rivers chimed in saying, Lady Marmalade got into the peanut butter again, referring to 30-year-old Aguilera who wore a black leotard under a jacket with heavy makeup, large hair and fishnet tights to the Michael Forever concert.

I'm looking at this and thinking, 'Well, she's put on weight. This just isn't flattering,' co-host George Kotsiopoulos said. But this is just a crappy outfit, regardless. No matter what shape your body is in, it's just bad.

Kotsiopoulos said Aguilera was probably still  a size 2/4, but Osbourne fired back.

Trust me, she said. I'm a 2/4. That is not a 2/4.

This is not the first attack on Aguilera from Osbourne, as the two have quarreled over the years. Back in August during an episode of again Fashion Police, Osbourne took her first stab at the starlet since her own 48-pound weight loss in 2009 while competing on Dancing with the Stars.

[Christina] called me fat for so many f---ing years, Kelly Osbourne said of the fellow 5 foot 2 inch celebrity. F--- you, you're fat, too, she went on, recorded on E!'s Fashion Police show. Maybe she is just becoming the fat b---h she was born to be.

What do you think about Christina Aguilera's weight gain? Is Kelly Osbourne being too harsh or is the singer getting fat? Sound off in the comments below.