The '22' hitmaker appears to have made the remark to close friend Selena Gomez as Harry's band One Direction were on stage at the Barclays Center in New York City to present the award for Best Pop Video.
While band member Louis Tomlinson, 21, was introducing the award, Taylor was filmed turning to the 'Come and Get It' hitmaker - who, ironically, was announced as the winner of the gong - and appeared to utter the words: ''Shut the f**k up.''
It's not clear whether the 23-year-old starlet made the foul-mouthed jibe, but she later poked fun at heartthrob Harry, 19, by dedicating her own award to him.
Taylor won the Best Female Video prize for her smash hit single 'I Knew You Were Trouble' - which was written about the One Direction star - and thanked the song's subject during her speech.
She said: ''I want to thank the fans because I tweeted about this a lot, I really wanted this.
''I also want to thank the person who inspired this song because he knows exactly who he is, because now I've got one of these.''
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