The 25-year-old had been performing at the KFC Yum! Centre in Louisville but then decided to take a visit to a nearby gay bar called Connections where a Gaga impersonator was on stage.
According to TMZ, she got up on stage in the middle of her track Born This Way and surprised the crowd, which was made up of male and female Gaga impersonators.
The fans went crazy as they saw their idol on stage, who was dressed in a similar outfit to the impersonator - tights and a black bra
The pair then sung part of the song together before Gaga took over.