Blake Shelton played Country Jam in Grand Junction, Colo. on Saturday night (June 18) and brought girlfriend Gwen Stefani to join him. The pop singer was with her man for his 40th birthday.

Stefani stepped onstage at the end of Shelton's two-hour set. The two sang their song "Go Ahead and Break My Heart," a duet that's featured on Shelton's If I'm Honest album. The crowd erupted the 46-year-old walked on stage unannounced, and of course, she looked wonderful.

Shelton turned 40 years old on Saturday and fans throughout Country Jam wondered if Stefani would accompany him to this headlining set. The rest of the performance stayed true to how he's performed throughout the spring and summer. In addition to songs from If I'm Honest, he played hits like "Honey Bee," "Austin" and "Sangria." "Go Ahead and Break My Heart" was the moment that stole the festival, however. They weren't done.

"This is fun!" he said. "Y'all have been so freakin' nice to me on my 40th birthday and I guess if I had one birthday wish for me personally ... I wish I could rock. 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."

Stefania was happy to oblige, returning to the stage by shouting "You want some of this?" The No Doubt singer then played her band's song "Hella Good," urging fans to jump up and down for her man's birthday. She left to let Shelton complete his encore, but not before a quick kiss.

During his Country Jam meet and greet, Shelton also shared with fans that Stefani decorated his plane in honor of his birthday.

See Pics of Blake Shelton & Gwen Stefani at Country Jam

Blake Shelton's Most Unforgettable Moments