The Leprous Lady could only be cured by a dish of warm blood from the right arm of a clean virgin who was a king’s daughter, and not just any virginal king’s daughter at that – they had to find the right one. Accordingly, every maiden damsel who passed by was forced to donate enough blood to fill a silver dish.
Near the castle was a graveyard full of tombs of damsels who had died by this custom. Twelve of those interred were king’s daughters; all who donated were apparently related in some ways to kings. It looks as if the people of the castle interpreted the position of king’s daughter rather loosely. Did they also so interpret virginity?
The custom was not always fatal. When Sir Balin and the lady of the slain Sir Herlews le Berbeus arrived at this castle, she survived being bled very nicely, leaving again after a night’s rest and “right good cheer”.
Sir Percivale’s sister Amide finally cured the Leprous Lady, giving her blood of her own free will. Amide died of it, and almost immediately thereafter the vengeance of God destroyed the castle and all its people.
See also
Castle of the Leprous Lady | The Legend of King Arthur