WHEN DID AHAZIAH BEGIN TO REIGN?

II Kings 8:25  In the twelfth year of Joram the son of Ahab king of Israel did Ahaziah the son of Jehoram king of Judah begin to reign. (KJV) II Kings 9:29  And in the eleventh year of Joram the son of Ahab began Ahaziah to reign over Judah. (KJV)

Both are true.  Joram was very ill for about a year, in which time Ahaziah began to take partial control over Judah.  Eventually, Joram died and Ahaziah became the sole ruler.  Not a contradiction.