I am not familiar with this particular story, but there are those who believe the currently reigning Royal family of Windsor (direct descendants of the Hanover Family)have surplanted the true successors to the throne which would be the more direct line of descendants in the Stuart family line,who were denied the throne only because they were Roman Catholics.

As for a King marrying a non-royal or illegitimate female; I doubt that would prevent any succession of his line. There is no "rule" persay that I am aware of that prevents an English King from marrying a commoner. After all, Henry VIII married more than one commoner; George VI was married to Lady Elizabeth Bowes Lyon and Prince Charles married both Lady Diana Spencer and Camilla Parker Bowles. The daughter of an Earl may be an "aristocrat," but she is still a commoner and not Royal. Edward VIII had to abdicate because he wanted to marry an American commoner that was "twice divorced." Had she been merely a "single" American commoner, she would probably have become Queen.
(Thankfullly she was not, since in the opinion of many that knew her she VERY Common in more ways than one)