2 Kings 11:1, 3-4, 21

When Athaliah, the mother of King Ahaziah of Judah, learned that her son was dead, she began to destroy the rest of the royal family.

Joash remained hidden in the Temple of the LORD for six years while Athaliah ruled over the land. In the seventh year of Athaliah’s reign, Jehoiada the priest summoned the commanders, the Carite mercenaries, and the palace guards to come to the Temple of the LORD. He made a solemn pact with them and made them swear an oath of loyalty there in the LORD’s Temple; then he showed them the king’s son.

Joash was seven years old when he became king.