'Three month' in the Bible

Jehoahaz was twenty-three years old when he became king, and he reigned for [only] three months in Jerusalem. His mother’s name was Hamutal daughter of Jeremiah of Libnah.

Jehoiachin was eighteen years old when he became king, and he reigned [only] three months in Jerusalem. His mother’s name was Nehushta daughter of Elnathan of Jerusalem.