Now that’s how you ring in the big 4-0! Gwen Stefani couldn’t resist planting a huge smooch on boyfriend Blake Shelton when she joined the country singer at his concert in Colorado as he celebrated his birthday on Saturday, June 18.

The No Doubt singer had just finished performing her smash hit “Hella Good” when she gave Shelton a shout-out on the mic — and then grabbed him for an extended lip-lock as fans cheered.

A clearly flustered Shelton couldn’t stop smiling as he addressed the crowd. “What just happened?!” he said. “I don’t know how I’m going to follow that.”

Gx

A photo posted by Gwen Stefani (@gwenstefani) on

Earlier in the night, Stefani joined Shelton on stage to sing their duet, “Go Ahead and Break My Heart.”

That time @gwenstefani SLAYED during @blakeshelton's #CountryJamCO set. #FestivalFever #HellaGood

A video posted by The Boot (@theboot_dotcom) on

Oh. My. God. #blakeshelton #gwenstefani #surprise! #CountryJamCO #FestivalFever

A video posted by The Boot (@theboot_dotcom) on

After the show, he took to Twitter to express his amazement over the picture-perfect night.

“I possibly witnessed the coolest thing of my life tonight,” he tweeted. “Thank you Colorado and @gwenstefani!!! Look up the videos!!”

Stefani, 46, made sure the birthday boy had a great day from start to finish. She kicked off the celebration with several posts to social media wishing her “favorite person” a happy 40th birthday (along with adorable throwback photos of the Voice coach as a toddler.)

Then, she decked out their private jet to Colorado with fun, colorful decorations that included Gwen and Blake–theme wine glasses (hand-painted with the outfits they wore on Oscar night) and streamers all throughout the cabin. After touching down in Colorado, they celebrated with cake, including one in the shape of a guitar.

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