Negotiations went right down to the wire between Britney and "X Factor" honchos. Her fiance, Jason Trawick, who you also see in the video, along with daddy Jamie Spears (not in video) signed the deal since they are Britney's conservators.
Britney didn't talk as she walked around her hotel -- the swanky Mandarin Oriental, but she did faintly nod affirmatively when asked if she was excited to work with Demi.
One funny thing ... In the clip you also see "American Idol" judge Randy Jackson, who says the additions of Britney and Demi to "X Factor" are "hot." Randy clearly knows where his bread is buttered.
FOX will make the announcement at the Upfronts today. Britney and Demi will be front and center.