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 ranks of baron and earl date to feudal, and perhaps Anglo-Saxon, times. The ranks of duke and marquess were introduced in the 14th century, and that of viscount in the 15th century. While peerages for life were often created in the early days of the peerage, their regular creation was not provided for by Act of Parliament until the Appellate Jurisdiction Act 1876.