How was King Joram of Israel killed?

Answer: Shot by Jehu's arrow

As Joram fled, Jehu drew his bow and shot him between the shoulders; the arrow pierced his heart.

“Joram turned around and fled, calling out to Ahaziah, “Treachery, Ahaziah!” Then Jehu drew his bow and shot Joram between the shoulders. The arrow pierced his heart, and he slumped down in his chariot.”— 2 Kings 9:23-24 (BSB)