Zac Efron, Ashley Tisdale Party on the Beach

By Alison Schwartz

07/03/2011 at 11:45 AM EDT

What did Zac Efron get longtime pal Ashley Tisdale for her 26th birthday?

A beachside piggyback ride!

The shirtless hunk, 23, was spotted giving his High School Musical costar a friendly lift as they marked the VnC Cocktails and Heineken Light-sponsored milestone Saturday in Malibu, Calif.

"So happy zacary made it to my party!" Tisdale, who sported a striped Mara Hoffman bikini, Tweeted. "He's my brother/best friend!"

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After frolicking in the sand – with buff and bronzed bods on display – Efron gave the birthday girl an encore piggyback ride as they headed back to a nearby friend's home to continue the festivities.