The Frog Prince (1986)

Princess Zora (Aileen Quinn) of the land of Tartonia feels lonely and sad, seemingly overshadowed by her prettier sister, Henrietta (Helen Hunt), and without many friends. While she's searching for companionship, she happens upon a man-size frog named Ribbit (John Paragon), who is actually a human prince who has been cursed into his current shape. As the pair bonds, Henrietta becomes spiteful of her sister's newfound happiness and tries to put an end to the blossoming relationship.