Created in England in 1337 under Edward
III who made his eldest son Edward
the Black Prince the Duke of Cornwall.
In England a Duke is the highest rank below a King or a Prince,
while in other European countries the higher rank of Archduke
or Grand Duke exists.
The first non-royal Duke was Robert de Vere, the Earl of Oxford,
who in 1386 was made Duke of Ireland.
The eldest son of the ruling monarch is made the Duke of Cornwall
and the second eldest the Duke of York.