This article original appeared on PEOPLE.
Swift, 26, joined the rapper, 41, onstage in a black off-the-shoulder crop top and matching mini skirt with white sneakers for a duet to Nelly’s “Dilemma.” Swift took on Kelly Rowland’s parts of the song and the two sang and danced as the crowd cheered on in approval.
This isn’t the first time Swift and Nelly have collaborated. Last year, Nelly joined the pop star on her 1989 stop in St. Louis, Missouri, and the two performed Nelly’s hit, “Hot in Herre” with Haim.
Kloss turned 24 last Wednesday, and Swift posted a selfie to commemorate her best friend’s big day.
“I LOVE YOU KARLIE,” Swift wrote in the Instagram post. “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!!! @karliekloss.”
Kloss also posted a photo on Twitter showing a beautiful sunset, bouquet of assorted flowers and Swift smiling on her iPad screen.
“When you’re halfway around the world & your best friend still finds a way to celebrate 24 with you @taylorswift13,” the model wrote in the post.
Kloss and Swift were introduced by mutual friend Lily Aldridge and hit it off almost instantly. Their last celebration together was Swift’s Fourth of July bash at her home in Rhode Island.
“People had been telling us for years that we needed to meet,” Swift told Vogue when the BFFs were featured on the cover in March 2015. “I remember makeup artists and hair people going, ‘God, she and Karlie would be best friends.'”