Gwen Stefani kisses Blake Shelton on stage at surprise birthday performance

Blake Shelton got one amazing birthday present!

The country singer, who turned 40 on Saturday (June 18), celebrated his milestone birthday by haveing his girlfriend, Gwen Stefani, make a surprise appearance onstage at the Country Jam in Grand Junction, Colo. Stefani, who was clad in a super sexy black corset and jeans, joined Shelton on stage for a duet of their song "Go Ahead and Break My Heart."

Then to add to the birthday fun, Gwen came back out for another song.

"I guess if I had one birthday wish for me personally ...; I wish I could rock," Shelton said before Stefani returned to the stage to sing No Doubt's Rock Steady single "Hella Good," according to Taste of Country. "I wish I was one of those type of artists that could rock but I can't ...; For my birthday I wish I could hear an artist who could rock, that's my birthday wish."

And then at the end of her performance .... she laid a big old kiss on him! The duo, who have been dating since November, rarely pack on the PDA in front of their fans making this one of the first on-stage smooches we know of.

Shelton screamed to the crowd after Gwen's big kiss, "I don't even know what just happened."

"I possibly witnessed the coolest and craziest thing of my life tonight.... Thank you Colorado and @gwenstefani!!! Look up the videos!!" he tweeted after the show.

Check out all of the social media posts of their big kiss and performance.

Here's Gwen's performance:

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PHOTOS: Blake Shelton and Gwen Stefani together