Simon Cowell — Britney’s OFFICIALLY On Board!! (and so Is Demi Lovato)

Breaking News0514_simon_cowell_britney_spears_Twitter
Simon Cowell
finally announced what we all knew was coming … Britney Spears is joining “X Factor” … and so is some other girl.

Cowell just tweeted a photo of himself with Britney, L.A. Reid and the show”s 4th judge Demi Lovato (pictured hovering awkwardly over Simon”s shoulder).

FOX just made the announcement at the Upfronts in NYC — where advertisers vie for commercial airtime on TV shows “up front” … several months before the shows actually premiere.

As we reported, negotiations between Britney and “X Factor” honchos went right down to the wire. Britney”s conservators — her fiance Jason Trawick and her dad Jamie Spears — signed the $15 million deal on her behalf.

Demi signed her deal immediately before Upfronts as well. It”s unclear how much she”s getting paid … but it”s fair to assume her paycheck”s gonna weigh a lot less than Britney”s.