King Richard of England had something similar. Some little siege of a random castle, got nicked by a crossbow bolt fired by some kid inside, which gave him something or other which killed him.
Must totally be what my teacher was talking about.
It has all the key elements: a king, a siege, an arrow/bolt, a superficial wound that leads to a disease, and an anticlimactic death. Sometimes, I think that history teacher just remembered the key elements, and gradually added random filler in between as he gave the lessons.
