Britney Spears - Britney Spears And Demi Lovato Celebrate L.a. Reid's Birthday On X Factor Set

Spears, along with Demi Lovato and Irish music mogul Louis Walsh - who is standing in for a sick Simon Cowell - surprised Reid at the Kansas City, Missouri round of auditions on Friday (08Jun12), a day after he turned 56.

The Toxic hitmaker presented her pal with a cake, and also serenaded him to mark his big day, according to E! News.

A source tells the entertainment news website, "L.A. was completely not expecting it. 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... It was totally unplanned for her to sing. We were all surprised!"

Lovato also presented Reid with a picture accompanied by the words 'LA & Demi - Bff - Besties' - and the record executive was touched by the gesture.

Uploading the drawing to his Twitter.com page, he wrote, "From my new bestie (best friend) ddlovato, thank you for the love."