|Changes in royal style
As a result of dynastic claims to the throne of France, Edward III, the grandson of the French King Philippe IV the Fair, occasionally used the title of King of France from about 1337. By commissions signed as "Rex Angliae et Franciae" and "Rex Franciae et Angliae" (6 Oct 1337) Edward III appointed the Duke of Brabant, the Marquis of Juliers, the Count of Hainault, and the Earl of Northampton his lieutenants and vicars-general in France. In the course of Hundred Years' War, Edward entered Flanders in January 1340 and the deputies of Ghent, Bruges and Ypres took oaths to him as their suzerain. He was proclaimed King of France with much ceremony in the Friday market of Ghent and a new great seal was fashioned and new royal arms assumed. The new regnal year of Edward III, which began on 25 Jan 1340, was styled the 14th of his reign in England, and the 1st of his reign in France.
According to the Treaty of Brétigny (8 May 1360) Edward III agreed to renounce the title of King of France and King Jean II to cede sovereignty over Aquitaine and Poitou. After the exchange of renewed promises of renunciations at Calais on 24 Oct 1360 Edward used a new seal on which the claim to the crown of France was omitted, and the use of double regnal dating ceased. However, the formal exchange of letters confirming the renunciations, timed to be made at Bruges on 30 Nov 1361, never took place.
After the successor of Jean II, King Charles V, broke the provisons of Calais and Brétigny, the Parliament of England agreed that the King should resume the title (3 Jun 1369) and Edward immediately gave orders that a new seal should be made. His 30th regnal year as King of France was counted from 11 Jun 1369 and ended 24 Jan 1370, together with the English regnal year. On 30 Dec 1369 Edward III issued a royal act confirming resumption of the title. [1; 2; 3; 4]