Niall Horan and Irish soccer star Robbie Keane backstage at a One Direction show last week at the Rose Bowl.Irish Voice.

One Direction heartthrob Niall Horan is officially legal in America, and he partied in Las Vegas last weekend to celebrate his 21st on September 13, according to reports.

The Westmeath-born teen idol hit the tiles with bandmate Zayn Malik and a few other pals in Sin City, not long after playing yet another sold-out 1D show, this time in Los Angeles at the Rose Bowl, capacity 90,000.

Harry Styles, the “leader” of the band, spoke about Niall’s birthday during one of the weekend shows. “Twenty-one years ago an Irish boy named Niall James was born … he liked to roam the fields in Ireland in a tractor and he liked to eat potatoes and stew,” said Harry, using every Irish stereotype in the book.

Styles said that Niall was also a very talented Irish dancer, and advised fans to be careful if they were out and about because he loves beer and would be “very very drunk.”

1D sang Happy Birthday to Niall while he danced a bit of an Irish jig, and all the fans happily joined in.

They’ll have more to be pleased about in November when yet another One Direction album hits the stands. Called Four, the first single is “Steal My Girl.” We can hear the ka-ching already.