Movie set in middle ages or mediaeval times

A young man is told to do a ceremony where he has a mask on and enters a cave there is a girl there also with a mask she has black hair
They mate and whatever.
He shows her his face so she knows who he is.
He knows her also but can’t tell because of the mask
They don’t speak at all to each other.
She ends up having a child a boy.
Fast forward few years I think he is king and the boy tries to kill him but he gets killed.