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.
Source: Wikipedia — Royal dukedoms in the United Kingdom (CC BY-SA 4.0)