2 Chronicles 36:10
And at the return of the year king Nebuchadnezzar sent, and brought him to Babylon, with the goodly vessels of the house of Jehovah, and made Zedekiah his brother king over Judah and Jerusalem. (ASV)
2 Kings 24:17And the king of Babylon made Mattaniah, [Jehoiachin`s] father`s brother, king is his stead, and changed his name to Zedekiah. (ASV)
Edit this section if you doubt error.
Maybe he was both his brother and uncle?