What does 1 Kings 22:51 mean?

Ahaziah, Ahab's son, became king over Israel in Samaria during Jehoshaphat's seventeenth year as king of Judah. He ruled Israel for two years. 1 Kings 22:51 - Modern Text Bible

(Ahaziah, the son of the infamous Ahab, starts his short reign over Israel while Jehoshaphat is still ruling Judah.)