The idea of Charlemagne marrying Irene pops up now and again. But what of this idea, aka: one of the opening moves for CK2 players.
Anthousa was one of the children of Constantine V by his 3rd wife. And she would go on to be a saint. But what if the Byzantine Emperor (either her father or brother) negotistes a political marriage with the rising Frankish ruler to the west?