How Britney Spears Behaved on Glee Set

Everyone's psyched for Britney Spears' guest-starring stint on Glee -- including the pop princess, who Tweeted a photo of herself on the show's set on Wednesday.

"From what I heard, she was really cool!" actor Harry Shum Jr. (who plays Mike Chang on the show) told UsMagazine.com at a Wednesday party for singer Samantha Marq's new single "I Like to Party" at a private L.A. home.

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"She was really excited to do the show. She watches it, so that's always nice," added Shum, who hasn't yet met the 28-year-old singer. "She was in and out real quick."

The actor was reluctant to share details on the episode, explaining that creator Ryan Murphy warned the cast not to leak anything. "I have to be extremely secretive," Shum told Us. "But it's going to be a fun one...I think this could be on par with the Madonna episode!"

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Any hints on the songs selected? "She has a lot of fun dance tracks," Shum teased.

Creator Murphy recently hinted that the "Circus" singer shows up as cast members hallucinate under anesthesia at the dentist, played by John Stamos.

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"He was so awesome!" Shum gushed of the former Full House star. "Just being able to sit there and be like, 'that is Uncle Jesse.' I don't get star struck, but he was like my babysitter when I'd sit and watch him as I was a kid."