"I have a friend from school in the audience tonight called Jack Robinson," Harry told the crowd between songs. "We're gonna get as quiet as we possibly can, and then on three, Jack Robinson is going to scream as loud as he possibly can."
Jack was a good sport about screaming and getting his face on the Jumbotron, but he had no idea what was about to happen next.
"I'm gonna tell you a quick little story before we do the next song," Harry continued. "When I was about 14 years old, Jack Robinson stole my girlfriend."
At the risk of inciting thousands of rabid, protective Directioners, Harry added, "If he's still here at the end of the show, feel free — little kicks, little digs on the way out."
Harry Styles embarrasses the guy who once stole his girlfriend
LAS VEGAS, NV - MAY 17: Singer Harry Styles of One Direction, winners of the Top Duo/Group and Top Touring Artist awards, poses in the press room during the 2015 Billboard Music Awards at MGM Grand Garden Arena on May 17, 2015 in Las Vegas, Nevada. (Photo by Jason Merritt/Getty Images)
CANNES, FRANCE - DECEMBER 13: One Direction member Harry Styles attends the NRJ Music Awards at Palais des Festivals on December 13, 2014 in Cannes, France. (Photo by Pascal Le Segretain/Getty Images)
SYDNEY, AUSTRALIA - NOVEMBER 26: Harry Styles poses with fans at the 28th Annual ARIA Awards 2014 at the Star on November 26, 2014 in Sydney, Australia. (Photo by Don Arnold/WireImage)
LOS ANGELES, CA - JANUARY 02: Harry Styles is seen at LAX on January 02, 2015 in Los Angeles, California. (Photo by Chinchilla/Bauer-Griffin/GC Images)
CANNES, FRANCE - DECEMBER 13: One Direction member Harry Styles arrives at the 16th NRJ Music Awards at Palais des Festivals on December 13, 2014 in Cannes, France. (Photo by Francois G. Durand/Getty Images)
MADRID, SPAIN - DECEMBER 12: Harry Styles of One Direction performs on stage during the '40 Principales' awards 2013 ceremony at the Barclaycard Center (Palacio de los Deportes) on December 12, 2014 in Madrid, Spain. (Photo by Carlos Alvarez/Getty Images)
LONDON, ENGLAND - DECEMBER 11: Harry Styles attends the Glam Rock Christmas party to celebrate the collaboration between House of Hackney and Terry De Havilland at The Scotch of St James on December 11, 2014 in London, England. (Photo by Keith Hewitt/GC Images)
LONDON, UNITED KINGDOM - DECEMBER 11: Harry Styles attends the BBC Music Awards at Earl's Court Exhibition Centre on December 11, 2014 in London, England. (Photo by Fred Duval/FilmMagic)
SYDNEY, AUSTRALIA - NOVEMBER 26: Harry Styles of One Direction arrives into Sydney on November 26, 2014 in Sydney, Australia. (Photo by KHAP/GG/KHAP/GG/BM)
LOS ANGELES, CA - NOVEMBER 23: Harry Styles of One Direction arrives at the 2014 American Music Awards at Nokia Theatre L.A. Live on November 23, 2014 in Los Angeles, California. (Photo by Jon Kopaloff/FilmMagic)
LOS ANGELES, CA - NOVEMBER 23: (L-R) Recording artists Niall Horan, Harry Styles, Liam Payne, Zane Malik and Louis Tomlinson of One Direction accept the award for Artist of the Year onstage during the 2014 American Music Awards held at Nokia Theatre L.A. Live on November 23, 2014 in Los Angeles, California. (Photo by Michael Tran/FilmMagic)
LOS ANGELES, CA - NOVEMBER 23: Singers Niall Horan (L) and Harry Styles attend the 2014 American Music Awards at Nokia Theatre L.A. Live on November 23, 2014 in Los Angeles, California. (Photo by Christopher Polk/AMA2014/Getty Images for DCP)
ORLANDO, FL - NOVEMBER 17: Harry Styles of the band One Direction appear on NBC's Today Show to release their new album 'Four' at Universal City Walk At Universal Orlando on November 17, 2014 in Orlando, Florida. (Photo by Olivia Salazar/FilmMagic)
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"Jesus Christ, Jack, that's no way to treat your friends," one of Harry's 1D bandmates chimed in before the boys kicked into the next song, "Little Things" (not the, perhaps more appropriate "Steal My Girl").