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
Apart from hereditary peerages, there exists peerages that may be held for life and whose title cannot be passed onto someone else by inheritance. The Appellate Jurisdiction Act 1876 and the Life Peerages Act 1958 authorise the regular creation of life peerages, with the right to sit in the House of Lords. Life peers created under both acts are of baronial rank and are always created under letters patent.