Nelly is the latest in a long, long list of artists to join Taylor Swift on stage on her 1989 tour although it is actually the fourth time he stage-crashed one of her tours.
Given her concert was taking place in his hometown of St Louis on Tuesday night it's not surprising he made his way on stage to perform his hit 'Hot in Herre' with the 'Shake if Off' star.
He also took the opportunity to perform his new single 'The Fix'. Haiim, who are supporting Swift on 198, also joined in.
As usual, Swift took to Twitter to share videos and photos of the collaboration, admitting they had rehearsed some moves prior to the performance, "Yes we made up a dance yesterday in the dressing room".