The Duke of Cornwall reference article from the English Wikipedia on 24-Apr-2004
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Duke of Cornwall

The Dukedom of Cornwall was the first dukedom created in the peerage of England. King Edward III created it for his son and heir-apparent, Edward, the Black Prince. (Prior to its creation, an earldom of Cornwall had existed.)

The dukedom remains one of the last in the United Kingdom still associated with an actual duchy (the other is the Duchy of Lancaster). Its income goes to the Duke (or to the monarch when the dukedom is vacant). The Duchy of Cornwall is separate and distinct from the political county of Cornwall and from the geographic region of Cornwall in southwestern Britain.

The Duke of Cornwall is the eldest son of the reigning monarch who is also the heir apparent. This would be the eldest living son if no older brothers left heirs. If no one meets these qualifications, the dukedom has either merged with the Crown (its holder has become monarch and has no eldest son who is heir apparent) or lapsed to the Crown (its holder has died and there is no living eldest son of the monarch who is heir apparent). The dukedom does not become extinct in either of these instances. A son becomes Duke of Cornwall when his parent takes the throne, or, if born to a reigning monarch, at the moment of birth.

This means that one can be the Duke of Cornwall without being the Prince of Wales, since the monarch confers the latter title explicitly, and often does not do so until the prospective Prince reaches the age of majority.

One can also become heir apparent without becoming the Duke of Cornwall (if one is not the child of the reigning monarch.)

Holders of the Dukedom of Cornwall, with the processes by which they became dukes of Cornwall and by which they ceased to hold the title:

Duke of Cornwall Parent From To
Edward, the Black Prince Edward III 1337 (Parliament) 1376 (death)
Richard of Bordeaux Edward, the Black Prince 1376 (charter) 1377 (acceded as Richard II)
Henry of Monmouth Henry IV 1399 (Parliament) 1413 (acceded as Henry V)
Henry Henry V 1421 (birth) 1422 (acceded as Henry VI)
Edward of Westminster Henry VI 1453 (birth) 1471 (death)
Edward Plantagenet Edward IV 1470 (charter) 1483 (acceded as Edward V)
Edward, Earl of Salisbury Richard III 1483 (father's accession) 1484 (death)
Arthur Tudor Henry VII 1486 (birth) 1502 (death)
Henry Tudor, Duke of York Henry VII 1502 (death of brother Arthur) 1509 (acceded as Henry VIII)
Henry Tudor Henry VIII 1511 (birth) 1511 (death)
Henry Henry VIII 1514 (birth) 1514 (death)
Edward Tudor Henry VIII 1537 (death) 1547 (acceded as Edward VI)
Henry, Duke of Rothesay James I 1603 (father's accession) 1612 (death)
Charles Stuart, Duke of York James I 1612 (death of brother Henry) 1625 (acceded as Charles I)
Charles James Stuart Charles I 1629 (birth) 1629 (death)
Charles Stuart Charles I 1630 (birth) 1649 (acceded as Charles II)
James Francis Edward Stuart James II 1688 (birth) 1689 (father's deposition)
George Augustus George I 1714 (father's accession) 1727 (acceded as George II)
Frederick Lewis George II 1727 (father's accession) 1751 (death)
George Augustus Frederick George III 1762 (birth) 1820 (acceded as George IV)
HRH Prince Albert Edward Victoria 1841 (birth) 1901 (acceded as Edward VII)
HRH Prince George Edward VII 1901 (father's accession) 1910 (acceded as George V)
HRH Prince Edward George V 1910 (father's accession) 1936 (acceded as Edward VIII)
HRH Prince Charles of Edinburgh Elizabeth II 1952 (mother's accession)  

Additional details appear in Cokayne, George Edward, The Complete Peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, Extant, Extinct or Dormant, A. Sutton, Gloucester, 1982. [orig. 13 volumes, published by The St. Catherine Press Ltd, London, England from 1910-1959; reprinted in microprint: 13 vol. in 6, Gloucester: A. Sutton, 1982 ]

See also: Duke of Rothesay