Gwen Stefani and Blake Shelton can are no strangers to serving up peak #CoupleGoals . The pair has been open about their whirlwind romance since it first began on The Voice. At Shelton's concert in Colorado on his 40th birthday this weekend, Stefani celebrated by joining him on stage and giving the country crooner a big ol' kiss.Stefani's short set was a surprise, according to Us Weekly . After Stefani, 46, performed "Hella Good," she leaned over and planted a kiss on Shelton. The birthday boy was clearly surprised by the whole thing: "What just happened?!" he said. "I don’t know how I’m going to follow that."