Britney Spears and Demi Lovato Celebrate X Factor Judge L.A. Reid's Birthday With Cake—and a Song

Pop stars gave a sweet treat to their X Factor panel mate

Now that's a pretty sweet treat.

Britney Spears and Demi Lovato teamed up to give their X Factor cohost L.A. Reid an extended celebration, by enjoying some cake—and a song—on the day after his actual birthday.

And that only added to the surprise. 

While Simon Cowell is out with bronchitis (and Louis Walsh is subbing), mega producer Reid kicked off the fun with his fellow X Factor judges Spears and Lovato in Kansas City. The "Hold It Against Me" crooner even surprised Reid with a cake, singing to him while she was at it.

"L.A. was completely not expecting it," a source on set told 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.'"

A source close to Spears said, "It was totally unplanned for her to sing. We were all surprised!"

Now that's a great birthday!