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ROYALTY AND NOBILITY

Capitalize a full title and a title before a personal name. Otherwise lowercase king, queen, duke, etc, including a title that is in apposition to a proper name.  

For British titles see Lord. Also consult a source such as Burke's Peerage or Debrett's Peerage.

            Queen Elizabeth; Elizabeth the Queen; Elizabeth II, Queen of England; the queen
            The queen opens Parliament next week.
            The former queen lives in quiet retirement.
            The present queen is Elizabeth II.
            the Queen of Great Britain and Northern Ireland
            Juan Carlos, king of Spain; the king of Spain; the king
            Carl XVI Gustaf
            the kings of France and England
            the former shah of Iran, the shah
            the Earl of Argyll, the fourth Earl of Argyll, the 12th Earl of Argyll, the earls of Argyll, the earl
            Queen Mother
            Prince Philip; the Duke of Edinburgh; the duke
            Prince Charles; Prince of Wales; the prince
            the Duke of Norfolk; the duke
            the heir apparent
            Emperor Augustus; the emperor Augustus