Forty and two years old was Ahaziah when he began to reign, and he reigned one year in Jerusalem. His mother's name also was Athaliah the daughter of Omri.
Forty and two years old - (cf. 2 Kings 8:26.) According to that passage, the commencement of his reign is dated in the 22nd year of his age; and according to this, in the 42nd year of the kingdom of his mothers family. 'If Ahaziah ascended the throne in the 22nd year of his life, he must have been born in his father's nineteenth year. Hence, it may seem strange that he had older brothers; but in the East they marry early, and royal princes had, besides the wife of the first rank, usually concubines, as Jehoram had (2 Chronicles 21:17); he might, therefore, in the 19th year of his age, very well have several sons' (Keil) (cf. 2 Chronicles 21:20; 2 Kings 8:17).
Athaliah the daughter of Omri - more properly, grand-daughter. The expression is used loosely, as the statement was made simply for the purpose of intimating that she belonged to that idolatrous race.