2 Chronicles 22
Ahaziah becomes evil king
Then Jerusalem made Ahaziah (Jehoram's youngest son) king in his place since the Arabians had killed all the other sons. Ahaziah was 22 years old when he began to reign, and he reigned for one year from Jerusalem. His mother's name was Athaliah (Omri's granddaughter). He also lived like Ahab, because his mother counseled him to do wicked things. He did evil in the Existing One's sight, just like Ahab's descendants had done. After his dad died, they were his counselors, to his own undoing. He even followed their advice and joined Jehoram (the son of Israel's King Ahab) in making war with Syria's King Hazael at Ramoth-gilead. The Syrians wounded Joram in battle at Ramah, so he returned to Jezreel to heal where Judah's King Ahaziah went to visit him.
Jehu kills Ahaziah
But God ordained that Ahaziah's downfall would come while he visited Joram. When he got there, he and Jehoram went to meet Jehu (Nimshi's son whom the Existing One anointed to destroy Ahab's lineage). While Jehu was executing judgment on Ahab's family, he met Judah's princes and Ahaziah's nephews (who worked for Ahaziah) and Jehu killed them. He looked for Ahaziah and eventually found him hiding in Samaria and killed him. They buried him saying, "His grandpa Jehoshaphat sought the Existing One with his whole heart." And Ahaziah's lineage had no one who could replace him on the throne.
Athaliah takes throne while Joash remains hidden
Now when Athaliah (Ahaziah's mother) saw that her son was dead, she rose up and destroyed Judah's entire royal family. But Jehoshabeath, (Jehoram's daughter & Ahaziah's sister) kidnapped Joash (Ahaziah's son) and hid him in a bedroom since they were about to kill him. Jehoshabeath successfully hid him in God's house with a nurse for six years while Athaliah reigned over the kingdom.