God chooses a new king for Israel and makes the killing of Ahab’s family his first assignment. Jehu does as he is told. In the process, Ahab’s treatment of Naboth is avenged in exactly the way God said it would be in 1 Kings 21.
God’s Word is always fulfilled exactly as He says. We are promised many things in the Bible and told of many future events, and we can trust His Word.