Jehoshaphat joined affinity with Ahab by marrying his son to Ahab's…

Jehoshaphat the son of Asa began to reign upon Judah.

1 Kings 15:24 (KJV)

Jehoshaphat was thirty and five years old when he began to reign; and he reigned twenty and five years in Jerusalem.

1 Kings 22:42 (KJV)

And in the third year of his reign he sent to his princes, even to Benhail, and to Obadiah, and to Zechariah, and to Nethaneel, and to Michaiah, to teach in the cities of Judah. And with them he sent Levites… and they taught in Judah, and had the book of the law of the LORD with them, and went about throughout all the cities of Judah, and taught the people.

2 Chronicles 17:7 (KJV)

It came to pass after this also, that the children of Moab, and the children of Ammon, and with them other beside the Ammonites, came against Jehoshaphat to battle.

2 Chronicles 20:1 (KJV)

And Jehoshaphat feared, and set himself to seek the LORD, and proclaimed a fast throughout all Judah.

2 Chronicles 20:3 (KJV)

O LORD God of our fathers, art not thou God in heaven? and rulest not thou over all the kingdoms of the heathen? and in thine hand is there not power and might, so that none is able to withstand thee?

2 Chronicles 20:6 (KJV)