Swift, Styles and Karaoke: Stars Sing Backstreet Boys in NYC (PHOTO)

Harry Styles and Taylor Swift gave unique performances on Monday night, bringing back the 90s with open karaoke performances.

Harry Styles and his One Direction band mates seemed to still have energy left over on Monday night following a concert at Madison Square Garden in New York City. The group followed their performance up with an encore at the Hudson Hotel. They were joined by Style's rumored new girlfriend, Taylor Swift, and Emma Roberts.

For one karaoke number, Swift, Styles, and Niall Horan joined each other on stage to perform a 1990s flashback of the song "I Want it That Way" according to reports. An eyewitness told E! News that Swift "spent the early part of the night hanging out with the parents, but once karaoke came on, she and Harry joined [other 1D members] onstage for the rest of the night."

Swift was in New York returning from a gala at which she received a reward from her ex Connor Kennedy's family. Both Swift and Roberts were joined by other girlfriends, according to the report. A fan also managed to capture a picture of Swift on Style on stage.

"Haylor is real, y'all," Sunny Jacob, a 1D fan, tweeted along with a picture of the couple. The two "were clearly having fun," an eyewitness told E! News. The group took turns at playing a game on Playstation before Styles and Swift headed back to Swift's hotel room hand in hand, according to the report.

The couple was spotted the next day, at around 11:30 a.m., leaving the Greenwich Hotel separately, according to E! News. The relationship between Swift, 22, and Styles, 18, has been questioned by both sides of fans. Swift fans have claimed that the star is "changing herself" for Styles; others have ridiculed her for dating an 18-year-old.