2 Chronicles 22:1

And the inhabitants of Jerusalem made Ahaziah, his (Joram's) youngest son, who probably assumed this name upon his accession to the throne, king in his stead, this being expressly mentioned because he was not the crown prince; for the band of men that came with the Arabians to the camp, the band consisting of Arabians which had plundered the royal domain, had slain all the eldest, thus leaving this son as the only legitimate heir of Jehoram. So Ahaziah, the son of Jehoram, king of Judah, reigned, he was proclaimed and accepted as king of the southern kingdom.