Final answer:
The animosity between Britain and France lasted for over a century during the Hundred Years' War.
Step-by-step explanation:
The long-standing animosity between Britain and France dates back to the Hundred Years' War, which lasted from 1337 to 1453. This conflict arose when England's King Edward III claimed the French throne after the death of French King Charles IV, resulting in a war that would span over a century. Although there were frequent truces during this period, the tensions and hostilities between the two nations persisted.