Wolfgang Holswig-Abenauer

Wolfgang Holswig-Abenauer is, depending on your source, the crown prince of The Empire or the nephew of Karl Franz through his sister.

Wolfgang in Death on the Reik is the nephew who is mentioned in a rumor to be imprisoned within his own castle by the order of Emperor Franz although the cause is not clear as the given reasons are that he has become a Chaos Mutant with a rat tail, has the plague, or is being protected from assassination attempts by his brothers.

Wolfgang in Beasts in Velvet and Drachenfels is the crown prince, and is a little boy that Genevieve Sandrine du Pointe du Lac Dieudonné protects from Drachenfels himself.

In Empire in Flames, a supplement for Warhammer Fantasy Roleplay is his nephew, and is an extremely mutated Chaos Mutant who has extended eyes like a slug, large bat wings, a bloated and misshapen face, and long claws.