Harry Styles and Taylor Swift received a "huge cheer" after performing a karaoke duet at One Direction's Madison Square Garden after-party.
After the British band performed at the iconic music venue in New York City on December 3 they headed out to a karaoke bar to celebrate.
Harry's rumoured girlfriend Taylor was in tow, and the twosome made sure all eyes were on them as they teamed up to perform a rendition of Kenny Rogers and Dolly Parton's Islands in the Stream.
"It was brilliant. There was a huge cheer when they got up," a source told British newspaper The Sun.
The country songstress also sang with the rest of the One Directions boys and Ed Sheeran on the popular 1998 Backstreet Boys' hit I Want It That Way.
Harry, 18, and Taylor were spotted holding hands and heading back to her hotel after the celebrations at 4am.
One Direction - also comprising Louis Tomlinson, Zayn Malik, Niall Horan and Liam Payne - cemented their status as reigning boy band in the UK and America as they performed to a screaming crowd of 20,000 fans at their sell-out show on Monday.
Niall thanked the fans for their continued support on stage, gushing: "This is the best night of our lives. You guys have travelled from all around the world and we cannot believe what has happened here tonight. Thank you so much."
Zayn added: "I'm overwhelmed. I'm from a small town in Bradford. Things like this don't happen to people like me. I owe it all to you."
One Direction are continuing their pop chart domination with their second studio album Take Me Home.
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