I gotta say that after your previous comment on this, my headcanon for this is something like the following:

Mary: You were having an affair with Elizabeth Villiers! I saw you leaving her room late at night!
William: I was totally not having an affair with her. We were exchanging diplomatic intelligence!
Mary: Uh-huh, likely story.
William: I mean, you know I couldn't have having an affair with her because... well... I prefer guys.
Mary: You... what? Wait. This explains a lot. Like the way you were all over my cousin Jemmy.
William: I mean, he's really hot. Don't deny it, you think he's really hot too.
Mary: ...Hmm. Let's think about this a little more.