NEW YORK, Aug. 8 (UPI) -- Taylor Swift joined Nelly onstage for an impromptu performance over the weekend.
The 26-year-old singer was attending model Karlie Kloss and oil heir Mike Hess' joint birthday party Saturday in the Hamptons when she teamed up with Nelly on his song "Dilemma."
Multiple videos online show Swift singing and dancing with the 41-year-old rapper. "Dilemma" appears on Nelly's second studio album, Nellyville (2002), and features Kelly Rowland on the original vocals.
Swift was also seen sharing a playful moment with Hess during the duet. She sauntered up to the birthday boy and kissed him on the cheek before briefly dancing with him and returning to the performance.
"Taylor was in an amazing mood, and super fun all night," a source told E! News. "At first she didn't want to perform but then Nelly asked her. Everyone was super into it. The crowd loved it."
Swift and Nelly previously teamed up on the rapper's song "Hot in Herre" in 2015. The pair performed the hit during Swift's 1989 tour stop in Nelly's home city of St. Louis, Mo.
Swift, whose boyfriend, actor Tom Hiddleston, was not present at the party, reportedly spent most of her time with Kloss. She had sent the model well wishes in an Instagram post on Kloss' actual birthday of Aug. 3.
"I love you Karlie!" she wrote. "You're such an exquisite person, always trying to make things better for others. Every day I'm inspired by how giving, loving, and thoughtful you are. Happy 24th birthday!"