Career
Josepha Seyffert was the issue of a secretary Seyffert from the Regierungsdikasterium, tax office, and Maria Franziska Reichard. In 1765, after the death of Françoise of Parckstein, the previous mistress of the elector, she attracted the attention of elector Charles Theodore at the opera in Mannheim and was made his mistress. Josepha von Heydeck was described as pretty, sensible, merciful and kind.
Upon the wish of the elector, she was discreet in her public appearances as Charles Theodore, though separated from his spouse electress Elizabeth Auguste, found it important that his spouse"s position as electress should not be undermined.
She was given her own house in Mannheim. She died in childbirth in 1771.