A royal mistress is the historical position and sometimes unofficial title of the extramarital lover of a monarch or an heir apparent, who was expected to provide certain services, such as sexual or romantic intimacy, companionship, and advice in return for security, titles, money, honours, and an influential place at the royal court. Thus, some royal mistresses have had considerable power, being the power behind the throne. The institution partly owes its prevalence to the fact that royal marriages used to be conducted solely on the basis of political and dynastic considerations, leaving little space for the monarch's personal preferences in the choice of a partner.
The title of royal mistress was never official, and most mistresses had an official reason to be at the court, such as being a lady-in-waiting or maid-of-honour to a female member of the royal family or a governess to the royal children. However, their real position was most often an open secret, and there was no real division between formal and informal political power in the early French court. From the 15th century onward and most importantly in France, chief mistresses gained a semi-official title (French: maîtresse-en-titre, literally "official mistress"), which came with its own assigned apartments in the palace. A chief mistress was also sometimes called a maîtresse déclarée, or "declared mistress". An unacknowledged, less important royal lover was known as a petite maîtresse ("little mistress").
