If there would actually be some civilizations in western europe at that time it would be plausable. But it was mostly barbarian. Not the barbarians were less inteligent or anything, but it takes a civilized man to rule a civilization.
But there are always theories, maybe he was plunder from a raid in the western europe or freed slave that showed high intelligence and understanding and was chosen over the predecesors biological sons, if there were any (to lazy to google it up) and there's always the atlantis theory
