Who was the last king of Judah?

Answer: Zedekiah

Nebuchadnezzar made Mattaniah king and renamed him Zedekiah; he reigned eleven years until Jerusalem fell and he was taken to Babylon.

“Then the king of Babylon made Mattaniah, Jehoiachin’s uncle, king in his place and changed his name to Zedekiah.”— 2 Kings 24:17 (BSB)