Britney Spears has serenaded L.A. Reid and surprised him with a birthday cake on an episode of 'The X Factor' USA.

The 'Toxic' hitmaker sang 'Happy Birthday' to her fellow talent show judge -- who turned 56 on June 7 -- with her fiancé Jason Trawick, after the pair presented the music mogul with a cake and candles backstage in the talent show's green room during the auditions stage of the competition in Kansas City.

In footage aired on the program on Wednesday, Sept. 19, L.A. said: "They don't have enough candles for my age."

He then told the 30-year-old singer: "You're the sweetest in the world, oh my God, thank you."

The Kansas auditions were held one day after the talent show judge -- who sits alongside Simon Cowell and Demi Lovato on the panel -- turned 56.

Cowell was unable to celebrate L.A.'s birthday in June, as he was ill at the time and Irish music mogul Louis Walsh had to stand in for him.

Britney has been no stranger to organizing birthday celebrations recently, after throwing a huge joint birthday party on Sept. 15 for her two sons, Jayden James, who turned six on Sept. 12, and Sean Preston, who turned seven on Sept. 14.

The blonde beauty hired a Sky High arcade and trampoline park in Calabasas, Calif. to celebrate her sons' birthdays. She invited 20 of the youngsters' friends to party, as well as Jason and her father, Jamie Spears.

It is not known if the children's father, Kevin Federline, attended the bash.