ET confirms through sources that Jennifer Aniston will make a guest appearance on NBC's Emmy Award-winning comedy "30 Rock." Aniston's last primetime acting turn was on her "Friends" co'star Courteney Cox's FX series "Dirt." No word on just what character she'll be playing on the Peacock Network's hit series topped by Tina Fey and Alec Baldwin. The third season of "30 Rock" premieres on Thursday, Oct. 30 at 9:30 p.m. Check back for more details on this developing story...

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