Royal dukedoms in the United Kingdom
In the British peerage, a royal duke is a member of the British royal family, entitled to the titular dignity of prince and the style of "His Royal Highness" who holds a dukedom. Dukedoms are the highest titles in the British roll of peerage and the holders of these particular dukedoms are Princes of the Blood Royal. The holders of the dukedoms are royal not the titles themselves. They are titles created and bestowed on legitimate sons and male-line grandsons of the British monarch, usually upon reaching their majority or marriage. The titles can be inherited but cease to be called "royal" once they pass beyond the grandsons of a monarch. As with any peerage, once the title becomes extinct, it may subsequently be recreated by the reigning monarch at any time.
Baron de Ros
Baron de Ros (pronounced "Roose") is the premier baron in the Peerage of England, created in 1288/89 for William de Ros, with precedence to 24 December 1264. (The spelling of the title and of the surname of the original holders has been rendered differently in various texts. The word "Ros" is sometimes spelt "Roos", and the word "de" is sometimes dropped.) "Premier baron" is a designation and status awarded to the holder of the most ancient extant barony of the Peerage of England. The present premier baron is Baron de Ros. Before the Dissolution of the Monasteries the Prior of the Order of St John in England was deemed premier baron.