James II of Scotland (1437-60)

It's interesting to note that James II of Scotland was the first to use artillery in his country or "understand its value."  It was a mixed blessing: it won him surprising victories against the powerful Douglases and their previously impregnable castles; but at the age of 30 against Roxburgh Castle and the English, a piece of cannon equipment flew off and smashed-in his face, killing him. (Massie: The Royal Stuarts)