Tonguez said:
There are only Two Royal Dukedoms in England
Duke of York and the Duke of Lancaster. Lancaster is always the Ruling Monarch (so Queen Elizabeth is the Duke of Lancaster (not Duchess)), and York is the Second Son (the First Son being the Prince of Wales - orignally designated so as to remind the Welsh of their defeat)
I am sorry, but that is not correct. For a start, you are leaving out the Duchy of Cornwall, which is held by the eldest son of the sovereign (even before his investiture as Prince of Wales).
And the duchy of York is not the title of the second son of the sovereign as such. The Queen made her second son Duke of York, but the title will be inherited by his sons, it will not pass to Prince Harry.
The duchy of York has been bestowed on many sons of sovereigns, as have the duchies of Gloucester, Richmond, Cumberland, Kent and a few others. And many times these lines have died out, the titles have reverted to the crown, and have been re-used. Or the senior line has died out, the dukes of York or whereever have inherited the throne, and the title has merged with the Crown. And been re-used.
And by the way, although there is a duchy of Lancaster, and although it is held by the Sovereign, there is no duke of Lancaster, because the Sovereign does not hold any lower hereditary titles: these become extinct on union with the Crown.
Regards,
Agback