What is the male version of a mistress?

The male equivalent of a mistress is often referred to as a "mister" or a "lover." Just like a mistress, a male lover is typically a person who is involved in a romantic or sexual relationship with someone who is already in a committed partnership or marriage. Men who act as misters may provide emotional, financial, or physical support to their partners, but their relationships are often kept secret or hidden due to the stigma associated with infidelity. In some cases, misters may also be referred to as "side pieces" or "boy toys." Overall, the concept of a male mistress or lover can vary depending on individual circumstances and cultural norms.