The royal families of Europe are all very closely related (one reason, perhaps, for their weak chins) so it won't really make any difference.  As for a "rightful Stuart king of Scotland", it's a bit like the sad pretenders to the Russian, French, Albanian thrones and so on; a monarch rules by consent, not by divine right, so there is no such thing as a rightful king or queen by accident of birth.  Go back far enough and we are all descended from "royalty"!

Malcolm