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18 December 2013, 10:14
The performance comes on the same day the couple debuted the official video for the track.
Katy Perry was seen taking to the stage during John Mayer's encore on stage at the Barclays Center in Brooklyn last night (17th December).
The couple performed their duet 'Who You Love' – taken from John's latest album 'Paradise Valley'.
The performance came on the same day the pair headed to Good Morning America to premiere the official video.
John introduced his girlfriend to the stage and gave her a kiss on the cheek before they both took to the mic.
Speaking earlier in the day, he admitted he jumped at the chance to work with Katy who has been extremely busy in 2013.
"That's the thing about working with somebody you love. You get to see them," he admitted. "I had to [make] a video in order to get to see my girlfriend."