2 Jehoram's brothers-the other sons of Jehoshaphat-were Azariah, Jehiel, Zechariah, Azariahu, Michael, and Shephatiah; all these were the sons of Jehoshaphat king of Judah. 3 Their father had given each of them valuable gifts of silver, gold, and costly items, and also some of Judah's fortified towns. However, he designated Jehoram as the next king because he was the oldest. 4 But when Jehoram had become solidly established as king, he killed all his brothers and some of the other leaders of Judah.
Matthew Henry's Commentary on 2 Chronicles 21:2-4
Commentary on 2 Chronicles 21:1-11
(Read 2 Chronicles 21:1-11)
Jehoram hated his brethren, and slew them, for the same reason that Cain hated Abel, and slew him, because their piety condemned his impiety. In the mystery of Providence such men sometimes prosper for a time; but the Lord has righteous purposes in permitting such events, part of which may now be made out, and the rest will be seen hereafter.