Katy Perry joins John Mayer onstage in New York

Rocker John Mayer sent fans at his New York concert into a spin on Tuesday (17Dec13) when he introduced his girlfriend Katy Perry to the stage as a surprise guest.

The couple made its first joint TV appearance on breakfast show Good Morning America early on Tuesday to unveil the video for the singers' new duet, Who You Love, and they put their relationship under the spotlight again that night as they performed the track together at the Barclays Center in Brooklyn.

The song featured as part of Mayer's encore, after belting out hits like Who Says and Wildfire, and as they wrapped up the tune, Perry planted a kiss on her boyfriend's cheek and hugged him before walking off stage.

She reappeared at the very end of the gig alongside Mayer and his entire band to take their final bows.

The pair has been dating on-and-off since August, 2012.