Duke

During the 19th century many of the smaller German and Italian states were ruled by Dukes or Grand Dukes. But at present, with the exception of the Grand Duchy of Luxembourg, there are no dukes ruling as monarchs. Duke remains the highest hereditary title (aside from titles borne by the reigning or formerly reigning dynasty) in Portugal (though now a republic), Spain, and the United Kingdom. In Sweden, members of the Royal Family are given a personal dukedom at birth. The Pope, as a temporal sovereign, has also, though rarely, granted the title of Duke or Duchess to persons for ``services'' to the Holy See. In some realms the relative status of ``duke'' and ``prince'', as titles borne by the nobility rather than by members of reigning dynasties, varied--e.g., in Italy and the Netherlands.

Question: do you have to be married to be a duke
Answer: no