2 Chronicles 22:1

And the inhabitants of Jerusalem made Ahaziah his youngest
son king in his stead
He being the only surviving one of the sons of Jehoram, the same with Jehoahaz, ( 2 Chronicles 21:17 ) who was saved when the rest were taken captive and slain, by his mother Athaliah, and he made his escape, and that she also escaped is clear from ( 2 Chronicles 22:10 )

for the band of men that came with the Arabians to the camp;
that is, of the Philistines, ( 2 Chronicles 21:16 ) , which band seems to be a band or company of thieves and robbers, as the Septuagint, cruel and barbarous, as the action ascribed to them shows:

[for they] had slain all the eldest;
sons of Jehoram; the Philistines and Arabians only carried them away captives, but those slew them in cold blood:

so Ahaziah the son of Jehoram king of Judah reigned;
being declared his successor by the inhabitants of Jerusalem.