Athaliah was the daughter of Israel's King Ahab and Jezebel. She married Jehoram, King of Judah with whom she had a son Ahaziah. When Ahaziah died at the hands of Jehu, Athaliah seized power and then proceeded to kill all members of the royal family.
When Athaliah the mother of Ahaziah saw that her son was dead, she proceeded to destroy the whole royal family. But Jehosheba, the daughter of King Jehoram and sister of Ahaziah, took Joash son of Ahaziah and stole him away from among the royal princes, who were about to be murdered. She put him and his nurse in a bedroom to hide him from Athaliah; so he was not killed. He remained hidden with his nurse at the temple of the LORD for six years while Athaliah ruled the land.
(2 Kings 11:1-3)
After a reign of six years Jehoida, a priest of Judah, led an insurrection. He crowned the young boy Joash king. When Athaliah heard the commotion, she rushed to the temple to see what was going on, ripping her robes and shouting, "Treason!"
Jehoida ordered her to be killed, but not in the Temple. The soldiers pursued her as she fled, finally putting her to death near the palace stables. Jehoiada and his followers immediately set about purging the land of the pagan idols before leading the new king to the throne.
Joash was seven years old when he began to reign.