Simon Cowell “Sad” Siobhan Magnus Was Kicked Off Idol

 Frederick M. Brown/Getty Images; Michael Becker/FOX

Simon Cowell looked sad after hearing that Siobhan Magnus was going home on Wednesday night's American Idol, a show witness tells

Also bummed at the news: fan favorite Crystal Bowersox, who bowed her head when the results were read, and Siobhan's sister, mom and friends, who cried through her exit song.

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(Siobhan was in the bottom three alongside Michael "Big Mike" Lynche and Casey James, who all got a group hug from Ryan Seacrest during a commercial break.)

When Siobhan sang her final screaming note, Simon was clearly smiling, even though he had turned away from her.

After finishing her song, the 20-year-old Cape Cod, Mass. resident gave Lee DeWyze a full body hug and stopped to talk to judge Kara DioGuardi, who went running up from her seat to say goodbye.

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In the audience: Cameron Diaz and Antonio Banderas, promoting their newest Shrek flick. Diaz spent the most time chatting with Ellen DeGeneres and Seacrest, while Banderas chilled with Randy Jackson.

"Cameron seemed in a great mood, laughing and smiling and waving at everybody," the witness says.

Wednesday night's Idol was full of performances. The Rascal Flatts rehearsed a song during a commercial break, and then spent some time chatting with Jackson. Shakira then hit the stage barefoot with Rascal Flatts.

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After the show wrapped, Lady Gaga pre-taped her performance in a set so elaborate, the crew spent three hours the night before building it. She seemed to be singing live, and was definitely playing the piano live. She rehearsed a few times. It airs on the May 5 episode.

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