Kelly Osbourne can't get enough of Christina Aguilera's weight gain, which was on display during the singer's performance at the Michael Jackson Tribute Concert.

The formerly chubby rock royalty showed her claws once again during a segment on E!'s Fashion Police devoted to Aguilera's ever-expanding frame, which Aguilera revealed in a terribly unflattering ensemble at the tribute concert.

She called me fat for years, Osbourne hissed. I was never that fat.

Fashion Police co-host Joan Rivers weighed in with her two cents: Lady Marmalade got into the peanut butter again.

A somewhat kinder George Kotsiopoulos tried to blame the Aguilera eyesore on the outfit, and added that the 30-year old singer was still probably a size 2/4.

Not so, says Osbourne.

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

During a Fashion Police segment this summer, Osbourne and co-host Joan Rivers dissected Christina Aguilera in a fuller figure-revealing dress, when Aguilera's weight gain was just beginning to become apparent.

Maybe she is just becoming the fat b--ch she was born to be, Osbourne said.

She looks like Snooki's Scandinavian cousin, Rivers piped in. It's a pretty dress but she's stuffed into it.

Osbourne and Aguilera have had a longstanding rivalry, which reportedly began when Aguilera mocked Osbourne at the 2003 MTV Europe Music Awards.

Osbourne is no stranger to weight struggles, and was known as the chubby, cranky kid when her family's reality series aired on MTV from 2002-2005. She has since dropped multiple dress sizes and adopted a much more ladylike look as she has joined the ranks of the Fashion Police.

According to Us Weekly, Osbourne lost 48 lbs. after appearing on Dancing with the Stars in 2009.

No one takes fashion advice from a fat person - they don't, Osbourne told Jay Leno  this summer when she appeared on Tonight Show with Jay Leno.

Unfortunately that's the world we live in.

During the same interview, Osbourne critized fellow Brit Kate Middleton for recycling outfits.

In England they are like 'look how thrifty she's being,' showing the British public that the Royals are in a recession as well. ... Only in this country they call it a faux pas, Osbourne said.

If I am going to be the future bloody Queen of England I'm going to wear that dress once because I'm giving up the rest of my life, all of my privacy, at least I can get a new dress every day.

In 2010, Osbourne complained to Us Weekly about the media attention focused on her weight.

I took more hell for being fat than I did for being an absolute raging drug addict. I will never understand that, she told the magazine.