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 In order to attach John, Duke of Brabant, to his cause, the king in 1339 proposed a marriage between the young Duke of Cornwall and John's daughter Margaret, and in the spring of 1345 wrote urgently to Pope Clement VI for a dispensation for this marriage. On 12 May 1343, Edward created the duke Prince of Wales, in a parliament held at Westminster, investing him with a circlet, gold ring, and silver rod. The prince accompanied his father to Sluys on 3 July 1345, and Edward tried to persuade the burgomasters of Ghent, Bruges, and Ypres to accept his son