That was quick.

After nearly a week of clubbing, partying and shopping in LA with new BFF, Paris Hilton, Us has learned exclusively that Britney Spears has abruptly pulled out of co-hosting with the heiress on the Fox Billboard Music Awards, scheduled to air live on December 4.

“She pulled out,” confirms a source with Fox. “She didn’t give a reason.”

The source tells Us that Hilton is still a possible host despite losing Spears as a sidekick. Other sources confirm that as recent as this morning, agents for both Hilton and Spears were hashing out the final terms of the contract, but at 5pm today, Spears had backed out of negotiations.

“We really don’t know the reason. But we’re disappointed she backed out.” says a Fox source.

The source says the show may go on with Hilton as solo host, or it may feature comedian (and Fox sitcom star) Brad Garrett, given he’s at the top of the show producer’s wish list.

At press time, neither Hilton or Spears’ reps were available for comment.

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