All men have something they would risk their lives to protect. Though the kingdom may crumble and the bonds between the Knights of the Round Table may break, King Arthur and Lancelot steel their resolve and clash their weapons. Titles matter not in this duel. They fight for their pride and for the sake of a woman.
A king is the sovereign head of a state, officially outranking all other individuals in the realm.
A knight is a person granted an honorary title of knighthood by a monarch or other political leader for service to the Monarch or country, especially in a military capacity. Historically, in Europe, knighthood has been conferred upon mounted warriors. During the High Middle Ages, knighthood was considered a class of lower nobility. By the Late Middle Ages, the rank had become associated with the ideals of chivalry, a code of conduct for the perfect courtly Christian warrior. Often, a knight was a vassal who served as a fighter for a lord, with payment in the form of land holdings. The lords trusted the knights, who were skilled in battle on horseback. Since the early modern period, the title of knight is purely honorific, usually bestowed by a monarch, as in the British honours system, often for non-military service to the country.
From the art and the storyline it looks like it is based on the fight of king Arthur and his knight Lancelot from the King Arthur myth.