John Gill Commentary 2 Kings 8:26

"Two and twenty years old was Ahaziah when he began to reign; and he reigned one year in Jerusalem. And his mother`s name was Athaliah the daughter of Omri king of Israel." — 2 Kings 8:26 (ASV)

Two and twenty years old was Ahaziah when he began to reign ,
&c.] In (2 Chronicles 22:2) he is said to be forty two years of age; for the solution of that difficulty (See Gill on 2 Chronicles 22:2):

and he reigned one year in Jerusalem ;
which was the whole of his reign:

and his mother's name was Athaliah the daughter of Omri king of Israel ;
that is, his granddaughter; for she was the daughter of Ahab the son of Omri, (2 Kings 8:18) , it was usual for grandchildren to be called children, sons and daughters, and perhaps she might be educated in the family of Omri.