Before anyone questions whether or not it's beyonce, you can clearly see red polish on the nails of her long, alien-like fingers. There is also a caption on the professional celebrity image site Getty Images, that states it's Beyonce on stage with Jay-Z.
To my understanding, At the end of Jay-Z's show he does a medley of songs that feature Beyonce, but Beyonce does not perform the songs with him. After this, the crowd yells and ask for Beyonce to come out and she never does. Well, this time she decided to surprise them in her disguise.
- concrete-loop.com