Mistress (lover)
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A mistress was a man's long-term female sexual partner and companion who was not married to him, especially used when the man was married to another woman.

In Sherlock Holmes Program 3A, the King of Bohemia had a mistress. A photograph of both parties together was intended to be used as blackmail. ()

In the mirror universe,  was a Trill soldier of fortune who worked for the Terran Rebellion. She was the lover/mistress of  until his death in 2371. ()

Gul Dukat, like many Cardassian officers during the Occupation of Bajor, conducted numerous affairs with Bajoran women, and had at least two mistresses, including Kira Meru, mother of Kira Nerys, and Tora Naprem, whom he claimed to love, and with whom he fathered a daughter, Tora Ziyal. () Damar also had a mistress. ()

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Illegal occupations