Which battle in 1356 saw the French king captured by the English during the Hundred Years’ War?

The story behind the answer

In 1356, an English force led by Edward, the Black Prince, shattered a larger French army; French cavalry assaults were funneled into unfavorable ground and cut down by disciplined, dismounted men-at-arms and volleys of longbow fire. Amid the collapse, King John II of France was taken prisoner on the field—an enormous blow to Valois authority.

His capture led to the Treaty of Brétigny (1360), imposing a vast ransom and ceding significant territories to England. With the monarch in English custody, France reeled from political instability and the depredations of “free companies.” For context, other famous victories—Crécy (1346) and Agincourt (1415)—also showcased English longbow tactics, while Sluys (1340) was a decisive naval clash early in the war.