Matthew Poole and continuators on 1 Kings 22:51

51 ¶ Ahaziah the son of Ahab began to reign over Israel in Samaria the seventeenth year of Jehoshaphat king of Judah, and reigned two years over Israel.

By comparing this Verse with ver. 41. it appears, that Ahaziah was made King by his Father, and Reigned in Conjunction with him a year or two before Ahab's Death, and as long after it; even as Iehoram the son of Iehoshaphat was made King by his Father in his Life-time, as we shall see hereafter; which possibly was done in compliance with Ahab's desire upon Marriage of his Daughter to Iehoshaphat's Son; and it may be Ahab, to induce and encourage him to do so, gave him an Example of it, and made his Son his Partner in the Kingdom.

Either after his Fathers Death: or one before it, and another after it.