Maîtresse-en-titre

The maîtresse-en-titre was the official royal mistress of the King of France.
The title was vaguely defined and used in the France in [the Middle Ages|Middle Ages] but finally became an acknowledged, if informal, position during the reign of Henry [IV of France|Henry IV], and continued through the reign of Louis XV. It was a semi-official position which came with its own apartments, estates and a title if the woman did not have any.
Some individuals having this position acquired significant power and more influence than the Queen of France, as some mistresses were known to advise the King of France in state affairs if he was so infatuated, broker favors for clients, elevate others in social mobility, forge alliances and negotiate with foreign diplomats.
In contrast, the title petite maîtresse was the title of a mistress who was not officially acknowledged.

French royal mistresses with the position of ''Maîtresse-en-titre''

While the king may have had many mistresses, there was normally only one official Maîtresse-en-titre. Below are examples of those with this position. For a full list of all the mistresses of a French king, regardless of their position as official or not, please see List of French royal mistresses.
Charles V