Christina Aguilera's weight gain is the only thing fans noticed after her amazing performance at the Michael Jackson Tribute concert Saturday, Oct. 8.

The 30-year-old pop singer performed Dirty Diana and Smile at the event, called Michael Forever. Her act was met with rave reviews, but her super skimpy outfit, which some felt made her look fat, was what got press tongues wagging.

The singer's weight has fluctuated over her years as a pop icon, and after her divorce from music producer Jordan Bratman in October 2010, she has been sporting a noticeably fuller figure. Over the last few months, Aguilera slimmed down again, earning nods for the weight loss.

Following her Saturday performance, however, Internet bloggers, commenters and publications all ripped into the singer, criticizing her choice to wear a leotard and fishnet tights with her very curvy figure.

Kelly Osbourne, commenting on the performance, went even further, slamming Aguilera after she claims the petite star mocked her for her own weight gain.

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[Christina] called me fat for so many f---ing years, reality-star 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.

Many tabloids have been careful to say that Aguilera's weight gain hardly makes her fat. But if that's the case, why is her weight gain, reportedly no more than 15 pounds, causing such a stir? Buzzfeed has posted an article of the Top 5 Most Frightening Pictures of Christina Aguilera, and comments on Twitter and Facebook run the gamut from she's a real person, get over it to that fat chick ate christina aguilera!

What do you think? Does Christina need to lose weight? Or should critics lay off her new curvy figure?