Selena Gomez - Selena Gomez Flies To L.a. To Join Justin Bieber's Surprise Birthday Party

The Baby hitmaker turned 18 on Thursday (01Mar12) and his manager Scooter Braun and mother Patti Mallette teamed up to throw a lavish bash at the Regent Beverly Wilshire Hotel on Friday to celebrate his age milestone.

Celebrity guests included pals Ashley Tisdale, Kim Kardashian, her half-sisters Kylie and Kendall Jenner, and boxer Mike Tyson, but there was one person Bieber was particularly stunned to see - his teenage sweetheart Gomez.

The singer/actress had been shooting Spring Breakers on location in Florida all week (ends04Mar12) and Bieber stuck by her side throughout the party as he covered her in kisses.

A source tells Usmagazine.com, "He was all over Selena the whole time, walking her around by the hand. He kept kissing her. It's clear she was the best part of the night for him. He is still so in love with her."

In addition to the surprise party, Braun also handed Beiber the keys to a brand new sports car. He unveiled the eco-friendly Fisker Karma to the car-crazy teen superstar during an appearance on The Ellen DeGeneres Show earlier in the week.