II Chronicles 35:19 Midrash

בִּשְׁמוֹנֶ֤ה עֶשְׂרֵה֙ שָׁנָ֔ה לְמַלְכ֖וּת יֹאשִׁיָּ֑הוּ נַעֲשָׂ֖ה הַפֶּ֥סַח הַזֶּֽה׃

In the eighteenth year of the reign of Josiah was this passover kept.

Read midrashic interpretation of II Chronicles 35:19: and classical rabbinic exegesis.