He had brothers, the sons of Jehoshaphat: Azariah, Jehiel, Zechariah, Azariah, Michael, and Shephatiah; all these were the sons of King Jehoshaphat of Judah.
References for 2 Chronicles 21:2
Their father gave them many gifts, of silver, gold, and valuable possessions, together with fortified cities in Judah; but he gave the kingdom to Jehoram, because he was the firstborn.
When Jehoram had ascended the throne of his father and was established, he put all his brothers to the sword, and also some of the officials of Israel.
Jehoram was thirty-two years old when he began to reign; he reigned eight years in Jerusalem.
He walked in the way of the kings of Israel, as the house of Ahab had done; for the daughter of Ahab was his wife. He did what was evil in the sight of the Lord.
Yet the Lord would not destroy the house of David because of the covenant that he had made with David, and since he had promised to give a lamp to him and to his descendants forever.
In his days Edom revolted against the rule of Judah and set up a king of their own.
Then Jehoram crossed over with his commanders and all his chariots. He set out by night and attacked the Edomites, who had surrounded him and his chariot commanders.
So Edom has been in revolt against the rule of Judah to this day. At that time Libnah also revolted against his rule, because he had forsaken the Lord, the God of his ancestors.
Moreover he made high places in the hill country of Judah, and led the inhabitants of Jerusalem into unfaithfulness, and made Judah go astray.
A letter came to him from the prophet Elijah, saying: "Thus says the Lord, the God of your father David: Because you have not walked in the ways of your father Jehoshaphat or in the ways of King Asa of Judah,