Cinderella: Conspiracy at the Emerald Castle (1996)

Still unaware that her new friend is Prince Charles, Cinderella must help him uncover the evil Duke Zaral's plot to overthrow the Kingdom. In order to seize power, the Duke plans to have Charles marry his daughter. When Charles refuses, the Duke hopes to ultimately eliminate the Prince by creating a double of him. Cinderella and Charles rush to thwart the Duke's evil plans before it's too late!