What is the opposite of mistress? [duplicate]

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.

Rather like mistress can refer to women connected to unmarried people but usually refers to a woman with a married man, the other man usually refers to a man with a married woman.

The Oxford English Dictionary gives this definition and these examples:

other man n. the lover of a married woman or female partner.

1886 R. Kipling Other Man in Civil & Mil. Gaz. 13 Nov. 3/3 They married her when she..had given all her poor little heart to another man... We will call him the Other Man.

1966 ‘S. Ransome’ Hidden Hour ii. 20 She had been here before. With the ‘other man’?

1994 Sunday Times 6 Mar. (Style & Travel section) viii. 4/1 He was cited by the Tory MP..as ‘the other man’ when he sued his wife..for divorce.

Other examples abound. There is the 2008 film The Other Man, in which a husband finds out about the other man in his now-deceased wife's life. (Side note: it's a bad movie.)

A recent popular romance novel called The Other Man has this on its first page:

For every hotwife and her husband, there's always the other man.

It definitely refers to a male partner from outside the relationship. In most usage, that relationship is a marriage.

Finally, what I particularly like about this phrasing is that its gender counterpart is so simple: the other woman.