Duchy of Cornwall from Duchy income, assisted by Grants-in-aid from the Queen. If there is no duke (for example, if the monarch does not have any male children) the duchy income reverts to the monarch and the annual Sovereign Grant is reduced annually by the amount of the duchy's income. The duchy was established on 17 March 1337 by the Royal Great Charter out of the former Earldom of Cornwall by Edward III for his son, Edward, Prince of Wales, the "Black Prince", who became the first Duke of Cornwall. The charter established that the Duke of Cornwall is to be the eldest
Edward the Black Prince differenced royal arms. His younger brother, John of Gaunt, used a similar shield on which the ostrich feathers were ermine. Edward's "shield for peace" is believed to have inspired the badge of three ostrich feathers used by later Princes of Wales. Edward married his cousin, Joan, Countess of Kent (1328–1385), on 10 October 1361. She was the daughter and heiress of Edmund, Earl of Kent, the younger son of King Edward I by his second wife Margaret of France. They had two sons, both born in Aquitaine: From his marriage to Joan, he also became stepfather to her children by