If a woman lies about her martial status and sleeps with a man is the man an adulturor as well?

I know that adultery is one of the most serious sins in the Torah. A sin so grave that there is almost no tschuva for it. But I am curious what happens when one part knows that they married and the other party doesn’t. Such as an example above where a woman decieved her lover that she had a kosher divorce. Is the man still liable?