A dwarfish and ill tempered French duke obsessed with questions of rank and genealogy. After Dudley Craig, Mary had married him, feeling that if she was going to keep a man, it might as well be a duke, so she became the Duchesse de Valençay. Jealousy may have played a role since Mary's sister Gerty (the youngest of the three Jonson sisters) was married to a grand duke (Vladimir).

Jean's role in the Jonson story was to disgrace himself, as a liar and a thief, a lecherous stepfather and tyrannical husband. While Mary lay dying of cancer, Jean threw a tantrum complaining that she was leaving him her houses, paintings and furniture only for his lifetime, as if he couldn't be trusted to leave them to the children (Eleanor and Nancy). Mary changed her will only for Jean to go back on his word and leave everything to his nephew.

Napolean had insulted an ancestor of the duke by calling him "a shit in silk stockings". Nancy, who loathed Jean because he had effectively disinherited her, liked to say that he had kept up the family tradition minus the silk stockings.