Hurry down the chimney tonight!

Katy Perry** was definitely feeling the holiday spirit on Christmas Day. The "Wide Awake" singer, 28, greeted her 30 million-plus Twitter followers on Tuesday Dec. 25 with a cute, sexy photo of her boyfriend John Mayer** in a Santa Claus costume.

"Santa Baby" reads the caption, in which the 35-year-old "Crossroads" crooner (who's missing the white beard) strikes a sultry pose in a red-and-white suit.

It's the most public display of affection yet for Perry, who has been dating Mayer for about five months (including a brief August split). Indeed, an insider tells Us Weekly that Mayer spent the Christmas holiday with Perry's family in Santa Barbara, Calif.

"They are seriously in love and exclusive," a pal recently told Us of the surprisingly resilient relationship -- Perry's first long-term romance since she and Russell Brand** finalized their divorce** in early summer.

"John is surprised at just how cool and smart she is," the pal says of the singer, whose exes include Jennifer Aniston, Jessica Simpson, Jennifer Love Hewitt and others. Says another friend: "John has proved he's matured and learned from his mistakes . . . Katy is blown away."

This article originally appeared on Usmagazine.com: Katy Perry Tweets John Mayer "Santa Baby" Picture