I just about this certain legend concerning an ancestor of Richard I. He is called Fulk Nerra “The Black”
He is described to be one of the most brilliant figures of French history, reigning for fifty three years. Though he was orphaned at eight, Fulk still grew up to be terrifying, at 14 he defeated the veteran fighter Conan of Rennes, by 17 he inherited his father's title of being Count of Anjou. But he is also subject to passionate moments that results in violent rage, extreme cruelty and just all around batshit crazy when the situation asks for it.
The legend I was interested in has nothing to do with wars and political intrigues though but actually pertains to he woman Fulk Nerra married or according to THIS source, his mother. It's is not surprising since legends tend to have many variations, but I'll stick with the Fulk Nerra one. I tried doing research online but surprisingly only a few related results showed up. This legend was quite known in the past, it's obviously either black propaganda, cover-up story or a tribute to the family's legacy of being truly memorable.
Fulk went on a journey without disclosing any destination, after some time he came back with a wife. The lady named Melusine, was significantly of unearthly beauty but of an unknown origin. Plus she had no relatives or friends, and was popular as "the dark princess of the forest.". She rarely attends Mass, but if she does, she is noticeable uncomfortable, leaving quite too early as she won't witness the consecration of the Host. This peculiar behavior and strange revulsion for the Mass aroused the suspicions of the Count's men. One day, they urged Fulk to compel her to stay in church. He reluctantly agreed. When she was about to leave, her way was blocked by four of her husband's men. They seized her, but she uttered a scream, shook her cloak off her shoulder, took two of her four children under her arms and flew out of the stained glass window of the church. She was never seen nor heard of again. This woman was said have been the one to have brought demon blood through the two younger sons she left behind, into the House of Anjou and later House of Plantagenet and all the the Angevin kings of England. Thus their unofficial saying / excuse for their actions "We who come to the devil must go back to the devil"