EDIT: HO-LEE FUCK, turns out one of my granddaughters is matrilineally married to the guy who is the heir to wait for it...West Francia AND The Byzantine Empire. OH MY GOD. And this isn't normal WF, no this is WF that ate Lotharingia AND Italy.
This is getting SOOOOO exploited. I have more then enough money to start spamming assassins, so I think that's what I'll do :3
Good luck!
Well turns out that...didn't go the way I hoped. For one thing the guy, while the son of both rulers, was only heir to Byzantine, I think for some reason WF had Seniority Succession....fuck if I know.
Anyway, none of that matters because both those empire-kingdoms goddamn IMPLODED shortly after my post. For quite awhile Europe from the upper edge of Spain to the west end of the eventual HRE and the tip of Italy was seemingly composed solely of petty duchies and counties.
Meanwhile Byzantium had a huge civil war that left it similarly broken (and apparently this was a war of succession, because the now-dead Empress had her eyes cut out and her heir-who-is-my-pawn came nowhere close to actually inheriting his birthright, and now there is some random dude on the throne) with only about half the Empire left, and the rest a slightly lighter pink
Now WF has returned and formed France, with about the same borders as France normally has, while Italy is now Lotharingia and Lotharingia is now Burgundy. And East Francia has about 5 counties to its name