Normally, we say
"He was caught with his mistress."
Here, we know that the male is a married person. The meaning is clear.
If he is not married, then we can say
"He was caught with his girlfriend."
But, how to convey that a married female was caught with her lover.
a female was caught with her ____.
Saying that, she was caught with her boyfriend does not clear the air that she is married or not.
So, is there any male-gender specific word opposite of mistress and clears the air that female is cheating her husband?
I googled few words: lover, sweetheart, loved one, love, beloved, darling, dearest, young man, man friend, man, escort, wooer, admirer etc.
And, from Wikipedia,
"Paramour" is sometimes used, but this term can apply to either partner in an illicit relationship, so it is not exclusively male.
But, none fits the requirement.