What really happened to anne Boleyn?

Answer 1

She was executed for treason (If a Queen had an affair it was called Treason), it's unlikely any of the cases against her were true.

She was one of the few people executed within the walls of the Tower of London. She was executed by an expert swordsman from France.

Answer 2

To clear the way for his third marriage which would produce an heir whose legitimacy would not be questioned