Katy Perry joined John Mayer on stage for a surprise appearance in Brooklyn.

The "Roar" hitmaker and her boyfriend sang their duet "Who You Love" from John's latest album Paradise Valley. They performed together on Tuesday at the Barclays Center in Brooklyn and even managed to sneak in a few kisses at the beginning of the song.

Hours before John, 36, and Katy, 29, sat down on Good Morning America for their first joint interview and premiered the music video for "Who You Love," which saw the couple kiss and embrace. John was initially hesitant to feature Katy on the track, saying, "My first thought was, 'You can't do that' and then the more I thought about just the music part of it, it made perfect sense. Even if I didn't know Katy, it would have made perfect sense.... For me it always had to be about the song ... It's a pretty big moving target to be a couple and have a song but I think there's an authenticity to it when you hear it."

Katy said about her duet with John, "It transcends us. It's more about the message of the song."