British claims to the French throne

From the 1340s to the 19th century, excluding two brief intervals in the 1360s and the 1420s, the kings and queens of England (and, later, of Great Britain) also claimed the throne of France. The claim dates from Edward III, who claimed the French throne in 1340 as the sororal nephew of the last direct Capetian, Charles IV. Edward and his heirs fought the Hundred Years War to enforce this claim, and were briefly successful in the 1420s under Henry V and Henry VI, but the House of Valois, a cadet branch of the Capetian dynasty, was ultimately victorious and retained control of France. Despite this, English and British monarchs continued to prominently call themselves kings of France, and the French fleur-de-lys were included in the royal arms. This continued until 1801, by which time France had no monarch, having become a republic. The Jacobite claimants, however, did not explicitly relinquish the claim.

The title was first assumed in 1340 by Edward III of England, the Kingdom of England being ruled by the French Plantagenet dynasty at the time. Edward III claimed the throne of France after the death of his uncle Charles IV of France. At the time of Charles IV's death in 1328, Edward was his nearest male relative through Edward's mother Isabella of France. Since the election of Hugh Capet in 987, the French crown had always passed based on male-line relations (father to son until 1316). There was no precedent for someone succeeding to the French throne based on his maternal ancestry, nor had there been a need to. There had been no shortage of sons for more than three centuries from the inception of the House of Capet until the early 14th century, when new precedents concerning female inheritance finally had to be introduced. On the death of Philip IV the Fair's son Louis X in 1316, immediately followed by that of his posthumous son John I, it had to be decided whether his young daughter Joan or his brother Philip would succeed to the throne. Philip arranged for his coronation, and became Philip V of France. He was challenged by the supporters of the Princess Joan, daughter of Louis X, on the basis of his right to the throne. In response, he convened an assembly of prelates, barons, and burgesses at Paris, who acknowledged him as their lawful king, and declared that "Women do not succeed to the throne of France." This was later said to have been based on the 5th century Salic law, but it is now known that the Salic Law was only rediscovered later and used by the lawyers of the Valois kings to fortify their masters' title with an additional aura of authenticity.

...
Wikipedia