In the Adventure Time episode " I Remember You " (S4E25), the Ice King and Marceline the Vampire Queen share a heartbreaking musical collaboration that reveals their shared, tragic past in the post-apocalyptic world. Marceline struggles as she tries to connect with the delirious Ice King, who, unaware of his history, finds old notes that reveal he once saved and raised her as Simon Petrikov before losing his mind to the crown. The emotional climax features them singing a song based on his old letters, highlighting their deep bond and his past sacrifice to protect her. You can find the episode streaming on Apple TV or Now TV . I Remember You | Adventure Time Wiki | Fandom