Even before Gwen Stefani joined Blake Shelton on stage at Country Jam Saturday night (June 18), the singer got a birthday surprise. Shelton headlined night No. 3 of the four-day country and camping festival in Grand Junction, Colo.

Fans left talking about the couple's performance of "Go Ahead and Break My Heart," a song they co-wrote for Shelton's If I'm Honest album. However, just before the birthday boy took the stage, fans in his meet and greet surprised him with a guitar-shaped birthday cake. After a round of "Happy Birthday," the singer posed for photos with fans. We cannot confirm rumors that Shelton had chocolate frosting on his lips as he mugged for photos.

A planned 90-minute set at Country Jam turned into nearly two hours of country fun, with Shelton singing hits from his entire catalog as he playfully teased the audience. At one point he urged the crowd to sing along with him, and then quickly said they were a little nasally. He teased the crowd earlier when they tried to sing him a birthday song. It came in parts, and never really turned into the singalong thousands were hoping for.

Fans were buzzing all day long that Stefani might be in the venue. No one set eyes on her until she walked on stage. However, earlier in the day she'd decorated his plane, and she took the photos of the cake and his celebration.

Watch Blake Shelton and Gwen Stefani Sing at Country Jam

See More Photos From Blake Shelton's Set at Country Jam