The Irish pop star took to the stage in Massachusetts on Saturday night (12Sept15) as part of the boy band's North American tour, and during the gig, he surprised fans by breaking into an impromptu cover of 22.

With guitar in hand, Horan said to the crowd at the Gillette Stadium, "It's my birthday in a couple of hours," before singing, "I don't know about you, but I'm feeling 22," as the audience joined him in singing the tune.

Later, Horan's bandmates led the fans in a rendition of Happy Birthday, as Harry Styles got down on one knee to serenade his pal, while Liam Payne and Louis Tomlinson also surrounded the birthday boy.

The concert marked the band's final headlining show in North America before they embark on an extended hiatus next year (16).