Little information about François de la Serre survives. A minor nobleman, he kept an estate in Versailles and a smaller house in Paris, and was known to be a close confidant of the King and of Mirabeau. His wife, Julie, died sometime around 1777, and De La Serre was left to raise his daughter, Élise, on his own. He died under mysterious circumstances in 1789.*
* You see this sort of whitewashing a lot when a notable Templar falls out of favor. Someone steps out of line, or fails to keep up with the time, and suddenly the rich tapestry that is a unique, lovely human being is reduced to a historical footnote about how terrible they are.
A bit like Americans and their celebrities, really.