And the inhabitants of Jerusalem made Ahaziah his youngest son king in his stead: for the band of men that came with the Arabians to the camp had slain all the eldest. So Ahaziah the son of Jehoram king of Judah reigned. (2 Chronicles 22:1)
The limited details presented leave the situation obscure. The royal princes were apparently in some camp away from the capital when they were beset by a marauding band of Arabs, and were captured and slain.