Adam Clarke on 1 Kings 13:11

An old prophet - Probably once a prophet of the Lord, who had fallen from his steadfastness, and yet not so deeply as to lose the knowledge of the true God, and join with Jeroboam in his idolatries. We find he was not at the king's sacrifice, though his sons were there; and perhaps even they were there, not as idolaters, but as spectators of what was done.