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Flame Princess (first name Phoebe and occasionally called FP) is the princess and ruler of the Fire Kingdom, as well as Finn's ex-girlfriend. When Jake asks Flambo if he knows any princesses that are Finn's age so he can fix his broken heart, he introduces Jake to Flame Princess. Flame Princess was locked away in a lantern in the main chamber of the Fire Kingdom when Jake first encounters her. It is later revealed that her father, the Flame King, put her there on Princess Bubblegum's advice when she was an infant, and she did not come out for 14 years. She has a short temper, trust issues, and a heat core that can destroy the world if overblown with emotions. She is also close friends with Cinnamon Bun. Due to the events in "Princess Day," she is considered a registered princess. As revealed in "Elemental", she is the current Fire Elemental.
- In the TV series she is voiced by Jessica DiCicco, who reprises her role in the game.
- Her appearance in the game is based on her Season 4 appearance.