When Taylor Swift takes the stage, you never know who is going to join her.
The "Blank Space" singer brought out Nelly as her surprise guest during her St. Louis, Missouri stop on the 1989 World Tour on Tuesday – and with the help of Haim, totally brought the house down!
Taylor, Nelly and Haim drove the audience wild with an amazing performance of the rapper's 2002 megahit "Hot in Herre."
WATCH: This Grandma Absolutely Freaked Out When Taylor Swift Welcomed Mick Jagger to the Stage
Decked out in all white Taylor and the girls of Haim – sisters Este, Danielle and Alana Haim –performed as backup dancers and singers as Nelly performed his classic.
In an Instagram video Taylor posted Tuesday night, she revealed that the dance moves were choreographed less than 24 hours ago! "Yes we made up a dance yesterday in the dressing room,” she wrote.
WATCH: Taylor Swift Denies Marriage Rumors to Calvin Harris With a Cheeky Tweet
This is the last night Haim was scheduled to join Swift on her tour after performing with the 25-year-old star since July.
Members of Haim were on cloud nine following their final 1989 show, tweeting about their unforgettable onstage moment with Nelly.
Nelly is just the latest big-name star to join T. Swift on stage. On Saturday night, Taylor brought out rock legend and The Rolling Stones frontman Mick Jagger during her second show at Nashville, Tennessee's Bridgestone Arena. The night before,Taylor was joined by Steven Tyler, Alison Krauss and Kelsea Ballerini. And during her record-setting five-show run at Staples Center in Los Angeles, California in August, she was joined by Justin Timberlake, Selena Gomez and Ellen DeGeneres.
NEWS: Taylor Swift Shares the Stage With Steven Tyler, Alison Krauss and Kelsea Ballerini in Nashville
On Tuesday morning, before getting to perform a beloved classic with Nelly, Taylor was busy denying rumors that she's planning to marry her boyfriend Calvin Harris. Check out the video below for more on Taylor's response to wedding rumors.