Anwn Ddu "the Black" ap Budic, King of Greece or Brycheiniog - So if this guy is a descendent of Saint Patrick

He wasn't actually born in Greece, if indeed he existed -- as you see from the other discussion thread, it looks like two Anwns have been conflated (at least) and the "rex grecorum" that is in one of the manuscripts comes from where we know not at the moment.

What is your source that says he is a descendant of St. Patrick?