Final answer:
Prince Prospero is killed by the masked stranger, which reinforces that death is inescapable, no matter one's wealth or power. This event in 'The Masque of the Red Death' embodies the theme that death is the ultimate equalizer.
Step-by-step explanation:
What happens to Prince Prospero when he confronts the masked stranger is that b) He is killed by the stranger. This moment is pivotal in Edgar Allan Poe's "The Masque of the Red Death" because it demonstrates that no matter how hard he tries to seal himself away from danger and death, Prospero cannot escape the inevitable. The theme of the story is developed through this event, illustrating that wealth and power offer no protection against death. It serves as a reminder that death is the great equalizer, which no precautions can avoid.