So he died according to the word of the LORD which Elijah had spoken. And Jehoram reigned in his stead in the second year of Jehoram the son of Jehoshaphat king of Judah; because he had no son. And Jehoram reigned in his stead - The Vulgate, Septuagint, and Syriac say, Jehoram His Brother reigned in his stead, in the second year of Jehoram. There were two Jehorams who were contemporary: the first, the son of Ahab, brother to Ahaziah, and his successor in the kingdom of Israel; the second, the son of Jehoshaphat, king of Judah, who succeeded his father in Judah. But there is a difficulty here: "How is it that Jehoram the brother of Ahaziah began to reign in the second year of Jehoram son of Jehoshaphat, seeing that, according to 2 Kings 3:1, he began his reign in the eighteenth year of the reign of Jehoshaphat; and, according to 2 Kings 8:16, Jehoram son of Jehoshaphat began to reign in the fifth year of Jehoram king of Israel?" Calmet and others answer thus: "Jehoram king of Israel began to reign in the eighteenth year of Jehoshaphat king of Judah, which was the second year after this same Jehoshaphat had given the viceroyalty to his son Jehoram; and afterwards Jehoshaphat communicated the royalty to Jehoram his successor, two years before his death, and the fifth year of Jehoram, king of Israel." Dr. Lightfoot takes another method: -
"Observe," says he, "these texts, 1 Kings 22:51 : Ahaziah the son of Ahab began to reign over Israel in Samaria the seventeenth year of Jehoshaphat king of Judah, and reigned two years; and 2 Kings 1:17 : And Ahaziah died according to the word of the Lord which Elijah had spoken, and Jehoram reigned in his stead, in the second gear of Jehoram son of Jehoshaphat king of Judah; and 2 Kings 3:1 : Now Jehoram the son of Ahab began to reign over Israel in Samaria the eighteenth year of Jehoshaphat king of Judah. By these scriptures it is most plain, that both Jehoram the son of Jehoshaphat, and Ahaziah the son of Ahab, began to reign in the seventeenth of Jehoshaphat; for who sees not in these texts that Jehoshaphat's eighteenth, when Jehoram the son of Ahab began to reign, is called the second year of Jehoram the son of Jehoshaphat? Now Jehoshaphat's reign was not yet expired by eight or nine years, for this was in his seventeenth year, and he reigned twenty-five years, 1 Kings 22:42; nor was Ahab's reign expired by two or three years, for this was in his twentieth year, and he reigned twenty-two years. 1 Kings 16:29. But the reason why both their sons came thus into their thrones in their lifetime, and both in the same year, was because their fathers, Jehoshaphat and Ahab, were both engaged in the war against the Syrians about Ramoth-gilead: and while they were providing for it, and carrying it on, they made their sons viceroys, and set them to reign in their stead, while they were absent or employed upon that expedition."
This is very probable, and seems well supported by the above texts, and would solve all the difficulties with which many have been puzzled and not a few stumbled, had we sufficient evidence for the viceroyalty here mentioned.