The fate of Josiah was unprecedented. No king of Judah had, up to this time, fallen in battle. None had left his land at the mercy of a foreign conqueror. Hence, the extraordinary character of the mourning (compare Zechariah 12:11-14).
Related Commentaries of 2 Chronicles 35:24
2 Chronicles 35:24
24 His servants therefore took him out of that chariot, and put him in the second chariot that he had; and they brought him to Jerusalem, and he died, and was buried in one of the sepulchres of his fathers. And all Judah and Jerusalem mourned for Josiah.