Britney Spears and her A-list guests were more ... together during the song — with Spears still in her wedding dress! — as Madonna held up a drink at the end in celebration.

Anticipating fan speculation, Spears clarified that the frilly look wasn't how she would be dressed to say "I do," writing: "No... this is not my wedding dress 👗 bahahah!!!!" Britney Spears ...

Spears, 21, and Aguilera, 22, then made an entrance from a giant wedding cake, dressed in wedding gowns and knee-length white boots. They ripped off their dresses and sang Madonna's hit Like A ...

Britney Spears' wedding to Sam ... Ahead of their upcoming wedding on Thursday, sources close to the couple tell PEOPLE that celebrities including Madonna, Paris Hilton, Selena Gomez, Kate Hudson ...

These pictures appear to show that Britney ... of Madonna's Like A Virgin hit. They then writhed around after ripping off the dresses to reveal hot pants and mini skirts - in what for Spears ...

RELATED GALLERY: Madonna, Drew Barrymore and More of Britney Spears' Celebrity ... together during the song — with Spears still in her wedding dress! — as Madonna held up a drink at the ...

Britney Spears is feeling ... twirled around to Madonna’s “La Isla Bonita,” rocking black heels and flipping her hair back and forth. At one point, she lifted her pink dress, playfully ...