Zenos was old enough that it's kind of odd he didn't have a wife or kids, given that all his ancestors back to Solus seem to have been married and reproducing at about 20. Someone claiming to be his secret girlfriend/wife who had his baby would be hard to disprove. Given what we know of Zenos, someone showing up claiming to be the mother of his baby who he was hiding from Varis would seem very unlikely, but I suspect they could sell it to at least some of the Garlean populace. If they wanted to get a member of the royal family (or at least someone who claimed to be part of the royal family) back on the throne, Zenos's Secret Baby would probably be the most effective strategy. Of course, then you sink into the political quicksand of figuring out who the regent ought to be until the kid's old enough to actually govern (Zenos is 26, he can't possibly have a child who's old enough to be running a country), whether this is actually Zenos's kid, what this should mean for the woman, and so on.