What is the male version of a mistress called?

A man who has a romantic or sexual relationship with a married woman is often referred to as a "lover" or "paramour." In some cases, he may be called a "mistress" as well, although this term is more commonly used to describe a woman in a similar situation. The male equivalent of a mistress may also be referred to as a "gigolo," "kept man," or "boy toy," depending on the nature of the relationship and the financial or material support provided by the woman. In many cultures and societies, the concept of a man being the "other man" in a affair with a married woman is viewed in a negative light and may be subject to stigma and judgment.