*NSYNC's Joey Fatone Kisses Nick Carter at Backstreet Boys Concert in Las Vegas -- Watch!

Yes, this really happened.

Joey Fatone was feeling extra affectionate on Wednesday night.

The *NSYNC member paid a visit to the opening night of the Backstreet Boys' Larger Than Life Las Vegas residency at the AXIS at Planet Hollywood, where he was given the VIP treatment -- and paid it back in spades.

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AJ McLean brought Fatone onstage during the group's romantic performance of "Shape of My Heart" -- where he, Nick Carter, Howie Dorough, Brian Littrell and Kevin Richardson gathered in a circle to deliver a personal, touching serenade. Fatone was clearly moved by the performance, and decided to express his appreciation with a passionate kiss -- on the lips of Carter!

"You're tearin' up the shape of our hearts tonight Joey Fatone ❤️," read the group's post on Facebook.

See the moment below:

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ET recently caught up with the Backstreet Boys at rehearsals for their residency gig, where they opened up about treating their career "like a marriage" -- but mentioned nothing about actually swapping spit with other boy banders.

"We go to counseling," Carter said, revealing that it was Dorough who came up with the idea. "We talk things out," he explained.

"It's so funny -- as time goes on, the issues kind of add up," he confessed. "But it's like family."

See more in the video below.