father
Nebuchadnezzar was "father" of Belshazzar in the biblical sense that David is called "father" of Jesus, (Luke 1:32). Belshazzar was probably a grandson.
Related Commentaries of Daniel 5:2
Daniel 5:2
2 Belshazzar, whiles he tasted the wine, commanded to bring the golden and silver vessels which his fathera Nebuchadnezzar had taken out of the temple which was in Jerusalem; that the king, and his princes, his wives, and his concubines, might drink therein.