I've never purposely tried to kill a king or an heir, but while I was playing the Vikings in VI, I would quite often just take a powerful army and romp across England. This was a good tactic, but one time while I was on one of these merry little walks, one of my heirs matures without me noticing. I move my king and the rest of my stack into the next territory, intent on raiding and my heir is attacked by a huge group of Northumbrian troops. I autocalced the battle for fun(once I realized what I was doing). He didn't win, but his huscarles did take 400 northumbrains with them to the grave