2 Kings 23:17

Then he said, What title is that that I see? And the men of the city told him, It is the sepulchre of the man of God, which came from Judah, and proclaimed these things that thou hast done against the altar of Beth–el.

Cross-reference

1 Kings 13:1 records the man of God's original prophecy against the altar of Bethel — the very prophecy Josiah is now fulfilling as he sees the tomb.

1 Kings 13:30 tells of the old prophet burying the man of God in his own tomb — that is the tomb Josiah sees with the headstone.

1 Kings 13:31 records the old prophet's request to be buried in the same grave — explaining why the tomb contains both prophets' bones, which Josiah spares.