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
The modern peerage system is a vestige of the custom of English kings in the 12th and 13th centuries; in the late 14th century, this right (or "title") began to be granted by decree, and titles also became inherited with the rest of an estate under the system of primogeniture. Non-hereditary positions began to be created again in 1867 for Law Lords, and 1958 generally.