Maîtresse-en-titre

The maîtresse-en-titre (French: [mɛtʁɛs ɑ̃ titʁ]) was the official royal mistress of the King of France.

[1] The title was vaguely defined and used in the Middle Ages but finally became an acknowledged, if informal, position during the reign of Henry IV (r. 1589–1610), and continued through the reign of Louis XV (r. 1715–1774).

It was a semi-official position which came with its own apartments, estates and a title if the woman did not have any.

[2] 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.

[3] From the reign of Louis XIV, the term has often been applied, both in translation ("official mistress") and in the original French, to refer to the main mistress of any monarch or prominent man when his relationship with her is not clandestine, e.g. Vibeke Kruse, Nell Gwynn, Jeanne Baptiste d'Albert de Luynes, Lola Montez, Magda Lupescu.