Nero's backstory is littered with hints that he's actually the lost son of vergil, and a former employee has even tweeted that this was supposed to be explored explicitly in the game, but was cut due to time reasons (along with dante's entire portion of the game, 3 bosses, and a complete story section that took dante through hell)
But that was off the record, and while the guy did work there, there was no way to verify if anything he said was true, since capcom made no comment on anything. Suddenly vergil is making an appearance in a special edition version of the game. I don't see this as a coincidence.