The WE WILL ROCK YOU star, 58, last visited Buckingham Palace in 2002, when the band performed Britain's national anthem GOD SAVE THE QUEEN on the roof of the royal building.
At today's meeting, the Queen referred back to May's performance for her Jubilee (50 year reign) celebration, saying, "It's a bit warmer down here than on the roof, isn't it?"
May says, "She was very charming.
"(Freddie Mercury) would have loved it. He would have been here. I think Fred's very proud."