When King Cygnus was defeated, his original title of Duke of Slytherin passed to his last living male relative, a nephew named Sirius Black. The nephew died without spouse or heirs, and the title reverted to his female cousin Princess Bellatrix, King Cygnus’ daughter. She is known for her caprices; she denied the title, and allowed its passage to her younger sister Princess Narcissa, who now holds the title Duchess of Slytherin in her own right – the first female to do so since its creation. Her husband, by right of his wife, is entitled to be addressed as Duke of Slytherin also.