Some lucky female fans were serenaded by the pop group as they played the One Direction hit over the loudspeakers during the concert.
After the show the Westmeath man tweeted: "Hahaha they play WMYB in the concert! hahaha! brilliant!" [sic]
The only Irish member of One Direction then got to meet the famous American pop band back stage, where they posed for a photo.
Niall tweeted the photo with the caption: "amazing night! met the backstreet boys and new kids! super nice guys! got some good advice!" [sic]
In addition to hanging out with the Backstreet Boys, Horan also attended a JLS concert in Sheffield.
Enjoying their down time, One Direction returned to the UK last week after a long tour of America, Australia, New Zealand, and Canada.