O único filho publicamente conhecido de Bill e Lucrezia (antes da história de Agatha acontecer) foi Klaus Barry Heterodyne.
De acordo com o velho senescal Carson , ele morreu na noite em que o Outro atacou o Castelo de Heterodyne, esmagado por caindo entulho como filho de Carson tentou tirá-lo do castelo.
Embora os eventos daquela noite tenham muitas dúvidas sobre eles, há pouco espaço para dúvidas sobre sua existência e morte. Spoilers ahoy:
Since what happened that night is a subject of extreme debate - Lucrezia was assumed kidnapped at the time, and that is now widely thought to be not true and that she in fact may have caused the events of that night - you can make arguments for just about anything happening. It's pretty clear Carson believes what he saw however, considering his own son was lost, and Bill Heterodyne himself went nearly nuts with the loss of both his wife and son.