Joan Rivers Tells Lady Gaga to 'Lighten Up' Amid Feud With Sharon, Kelly Osbourne

Ganging up on Gaga! One day after Sharon Osbourne came to daughter Kelly's defense by way of a scathing response to criticism from pop star Lady Gaga, Kelly's co-host Joan Rivers has joined the fight.

In an interview with Entertainment Tonight, the 79-year-old comedienne addresses the "Born This Way" singer's recent claims that "Fashion Police" -- the E! style series on which Rivers, Kelly, Giuliana Rancic, and George Kotsiopoulos comment on the do's and don'ts of celebrity fashion -- is mean-spirited. According to Gaga, the show is just an excuse to bully other stars.

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"'Fashion Police' is a comedy show; anyone that comes out of an egg should figure that out," Rivers tells ET, alluding to Gaga's Grammys appearance in 2011, when the singer was carried onto the red carpet in a giant egg-shaped vessel. She goes on to say that the pop star should "lighten up" and focus on using her celebrity to draw attention to more important issues.

Gaga's comments were part of an open letter she posted to Kelly Osbourne on Thursday, Jan. 10, in response to something the "Fashion Police" standout, 28, said about the singer's fans being "the worst" when it came to bullying. ("They've said I should kill myself, that they hope I get raped," the reality star told Fabulous magazine.)

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"I have empathy for you Kelly, but I feel it culturally important to note that you have chosen a less compassionate path," Mother Monster wrote in her letter. "Your work on E! with the 'Fashion Police' is rooted in criticism, judgment, and rating people's beauty against one another. 'Appearance' is the most used reason for bullying in the world. Your show breeds negativity, and over the years has even become comedic in nature. It glorifies you and Joan Rivers pointing in the camera, laughing, and making jokes about artists and celebrities as if we are zoo animals."

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Sharon Osbourne fought back on her daughter's behalf a short time later, calling Gaga a "bully" and a "hypocrite" for posting the letter under the guise of seeking "a kinder and braver world."

"You know it would have been much more dignified of you to do this privately," Osbourne said in a note on her Facebook page. "I am calling you a bully because you have 32 million followers hanging on your every word and you are criticizing Kelly in your open letter. Are you so desperate that you needed to make this public?"