Sunday marked the awards' return to London for the first time since 1996, and locally bred singer Rita Ora was a suitably chipper host. "Holding Me Back" had already won the EMA for best song earlier in the evening, with Mendes thanking his "best friends, Teddy [Geiger], Scott [Harris] & Geoff [Warburton], for writing this song with me".
The Irish band dedicated the award to label boss Chris Blackwell of Island records, who signed them nearly 40 years ago.
The evening was opened by United States rapper Eminem, with a duet with Skylar Grey on the song Walk on Water.
Singer Camila Cabello, who won the best-pop prize, performed "Havana" with a troupe of dancers dressed as bathing beauties around a realistic projection of a pool. Winners are selected by fans across the continent.
Louis Tomlinson, from the boy band One Direction, landed the best United Kingdom and Ireland act.
Eminem was also named best hip-hop artist, and proclaimed surprise.
Ed Sheeran won Best Live Act and Best Rock went to Coldplay.
U2 were crowned the Global Icon, with Bono singing a burst of Stormzy's "Blinded By Your Grace" as they collected the trophy.
"U2's impact on music, pop culture and social issues around the world has been tremendous", said Bruce Gillmer, producer of the awards ceremony. U2, recipients of the global icon award on the night, performed "Get Out of Your Own Way" from Trafalgar Square.
Swift has nominations in six categories at the music awards, including best artist and best video, for "Look What You Made Me Do".
British singer and actress Rita Ora took charge of the ceremony and also turned in a popular stage performance.
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