My illegitimate ancestor was the son of a nobleman of a small city in Europe (not in Britain)--the nobles seem to have had lots of illegitimate offspring but often took care of them. In the case of my ancestors they were set up as architects.
European royalty tended to have lots of illegitimate children by their mistresses--during the reign of Charles II of England, people who didn't want his younger brother to become king made an unsuccessful attempt to have one of Charles' illegitimate sons made the successor.
He’s up my tree, but then, so is Alfred the Great, Charlemagne, all thanks to my “gateway ancestor”. That’s a different line than my personal bastard. :^)