Taylor Swift and Haim improvised a dance to perform during Nelly's 'Hot in Herre' in St. Louis on Tuesday (29.09.15).

The rapper joined the 'Days Are Gone' singers as a special guest at the Scottrade Center for the latest stop on Taylor's '1989' world tour and Taylor was so excited she and Haim made up some dance moves in their dressing room.

As Nelly sang, Este, Danielle and Alana Haim - who wore white dresses that matched the pop star's skimpy playsuit - and Taylor performed as backing singers for him.

Taylor posted a video to Instagram and wrote: ''HOT IN HERRE

@derrtymo feat @haimtheband. Yes we made up a dance yesterday in the dressing room (sic).''

Haim - who are good friends with the 'Bad Blood' singer - took to social media afterwards to thank both stars.

They wrote: ''The highlight of our friendship thus far @HAIMtheband PS WE LOVE YOU @Nelly_Mo

#1989TourStLouis (sic)''

And Nelly wrote: ''She always puts on the best shows and Tonight show was [email protected] thanks for rocking #THEFIX (sic).''