Merlin said the woman who looks like Her Majesty, she's the reason that King Arthur died. She tried to kill him and condemned him even after he gave her a chance to repent, because she couldn't forgive him for the ban on magic. And she was the one that Mordred loved. [And, well, you know the rest of the legend having to do with that.]
He wanted to know what Her Majesty was like. If she was a good person.
I couldn't tell him much. I don't know her, but I know enough she isn't like the woman he described.