In the English or British court, a royal mistress is a woman who is the lover of a member of the royal family; specifically, the king. She may be taken either before or after his accession to the throne. Although it generally is only used of females, by extrapolation, the relation can cover any lover of the monarch, whether male or female. Queen Elizabeth I is said to have had many male favourites, including Robert Dudley, 1st Earl of Leicester, although it is not known whether the relationships were sexual or not.
Monarchs have had an incentive to take mistresses in that they generally made dynastic marriages of convenience, and there was often little love in them.[1]
Beyond the physical relationship, the royal mistress has often exercised a profound influence over the king, extending even to affairs of state. Her relationship with the queen consort could be tense, although some wives appear to have felt little jealousy in the matter.[2]