While they do look rather similar, it's much more likely that his father was Rance.
After all, Rance has technically counted as nobility occasionally, is a complete and utter bastard the majority of the time, and he greatly enjoys building up harems.

A series of hentai-type fantasy RPGs featuring the "hero" Rance, where along with the usual fantasy adventure stuff, he also has a lot of sexual escapades, with quite a bit of those escapades, but nowhere near most of them, involving raping women into submission.
He also does a lot of non-sexual horrible things to the general populace wherever he goes, all because he views being the designated "hero" of his world as giving him free reign to do whatever he wants.

It's definitely not a game series for everyone.