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.
Peerages in the United Kingdom
Within the members of each rank of the peerage, peers of England precede peers of Scotland. English and Scottish peers together precede peers of Great Britain. All of the aforementioned precede peers of Ireland created before 1801. Last come peers of Ireland created after 1801 and peers of the United Kingdom. Among peers of the same rank and Peerage, precedence is based on the creation of the title: those whose titles were created earlier precede those whose titles were created later. But in no case would a peer of a lower rank precede one of a higher rank. For example, the Duke of Fife, the last non-royal to be created a duke, would come before the Marquess of Winchester, though the latter's title was created earlier and is in a more senior peerage (the peerage of England).