The Prince of Wales is the title which is given to the king’s (queen’s) eldest son when he becomes 18. The origin of this title goes back to the time of Edward I. When Edward I destroyed Welsh independence in the war of 1282 -1283, he created an unwritten law making the eldest son of an English king the Prince of Wales. The king’s son inherits the title of Prince of Wales at a special ceremony and automatically is pronounced king when the old king dies. Hence we have the saying:
«The king is dead, long live the king!»
Since 1337 the king’s eldest son has been bom the Duke of Cornwall. Cornwall was a Celtic territory created by Edward in who gave his eldest son the Black Prince that title.
Thus the eldest King’s son has been bom the Duke of Cornwall and at the age of 18 receives the title of Prince of Wales, a Regent is appointed to rule the country until the Duke reaches the age of 18.
This tradition still lives though it is not quite popular in Wales.