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.
History of the British peerage
During the reign of Henry VIII, peers attempted to consolidate and secure their position. They declared themselves "ennobled in blood," and suggested that no peerage could be extinguished except by an Act of Parliament, upon the extinction of all heirs to it, or upon forfeiture for treason or felony. The Spiritual Lords had attempted to secure the privileges of the Peerage while maintaining their ecclesiastical privileges, but lost in both attempts. Nonetheless, they were in the majority in the House of Lords until the Dissolution of the Monasteries, which removed the abbots and priors from the House. Thereafter, the temporal peers formed for the first time a majority in the Lords.