Ypomenés
King of Britain and the grandfather of the Questing Beast.
His daughter loved her brother, named Galahad. She was impregnated by a demon. Under the demon’s influence, she falsely accused Galahad of rape. Galahad was executed, and the Beast was born of Hipomenes’s daughter in due time. Realizing that the monster couldn’t have sprung from a human, Hipomenes tortured the truth from his daughter and then had her executed.
See also
Dusius | The Legend of King Arthur
Incubus | The Legend of King Arthur
Succubus | Myths and Legends