2 Kings 8:27

And he walked in the way of the house of Ahab, and did evil in
the sight of the Lord, as [did] the house of Ahab
Worshipping the calves, and Baal also:

for he was the son in law of the house of Ahab;
he was the son of Jehoram, who was son-in-law to Ahab, having married his daughter, which accounts for his being guilty of the same idolatrous practices.