He Really Can Act: The film may only be 25 minutes, but Wayne Allwine utilizes them to really bring out the emotion in both Mickey and the Prince, especially in the scene where the king dies.
Moral Event Horizon: This version of Pete threatening to kill Pluto and abusing his power under the name of the king.
Tear Jerker: The old king's death. Not only did he die unaware of his captain's atrocities in his name, he just seemed so broken, and he doesn't even know he's talking to an impostor and not his son.
Mickey didn't have the heart to tell the dying king.
It also applies to the Prince who didn't find out about his father's death until a passing boater informed him. The grief of losing his father was hard enough, but it was also coupled with the fact that he wasn't there to say good-bye. His long silence after hearing the news made it apparent.