Fun fact: Jewish physicians were the only scholars in Europe who had a reliable way to deal with the greatest disease of the time: Karlings!
Step one: Convert the nearest Karling
Step two: Watch as angry vassals and the pope throw everything but the kitchen sink at them.
I had a converted grandson of Charles ruling Francia in my game. He was deposed once by vassals and once by crusade, both times fleeing to court in Asturias and then systematically assassinating his cousins to get back on the throne. He had one son that died very young and two daughters that were married off so once he died during his third reign there was no Karling left.
I was watching this from Brittany with some interest (and alarm) and did not actually involve myself in it, it was purely ai-driven emergent drama and I loved it