It looks like Queen Britney Spears is getting more and more comfortable on 'X Factor' -- minus the little snafu of tripping and almost eating pavement in her high heels after she exited her car for the Kansas City, Missouri auditions.

Britney and Demi Lovato joined forces to treat L.A. Reid to a little cake and song for a birthday celebration the day after his actual birthday. And it was B who performed the little song number while presenting Reid with his cake.

"L.A. was completely not expecting it," said a source on the set of the show to E! News. "He was trying to keep his birthday kind of a secret but at the end of their break, Britney surprised L.A. with a huge chocolate cake while singing 'Happy Birthday.' It was cute. Demi drew him a picture saying 'LA & Demi -- BFF – Besties.'"

Too sweet! Someone who wasn't as sweet as usual? Brit-Brit, who sources told TMZ was tougher than usual without Cowell around. She even told one Elvis-impersonating hopeful, "Your look was a little much, and everything was messed up. But I found you interestingly entertaining." Dang!

So uh ... how much would it cost to have Britney sing at our birthday?

Watch the 'X Factor' Season 2 Promo