Dragonheart (1996)

Bowen, a young knight dedicated to the Old Code of Honor of King Arthur, serves his queen by tutoring her son Einon in ethics, morality and swordsmanship. The king is slain during a massacre of rebellious villagers, and a peasant girl causes Einon to fall on a wooden stake which impales his heart. Bowen and the Queen Mother take the dying Einon to a magic cave where a mystical dragon, Draco, saves his life in exchange for Einon promising to live by King Arthur's code. But King Einon betrays his promise and becomes a murderous, arrogant tyrant. When Bowen, now an errant knight, befriends Draco, he learns that in order to kill the evil king, the great dragon must die. For the part of his heart he gave to save the unworthy Einon is now protecting him. Draco's gravest concern is not at dying, but at losing his soul. Ultimately, the moment comes when Bowen must gather his courage to give Draco the death he desires, which will end the evil of King Einon, and allow Draco's soul to join the stars.