Divrey Hayamim Bais 22:9

And he searched for Achazyahu, and they captured him while he was hiding in Shomron (Samaria), and brought him to Yehu; and when they had slain him, they buried him. Because, they said, he is a ben Yehoshaphat, who sought HASHEM with all his levav. So the Bais Achazyahu had no koach to retain the mamlachah (kingdom).