His third appearance, which also marked his first major appearance, is in "The Prince Who Wanted Everything." His character was written by Lumpy Space Princess, who dreams to be with him. In the episode, Lumpy Space Prince is depicted as a Marty Stu character, being described as an altruistic, philanthropic, selfless, and incredibly handsome prince who feeds his people gold-painted sandwiches as "presents." His parents, however, are slobbering monsters who desire the prince to be a monster and force him to eat worms and sharpen his teeth. As a result of disobeying them, Lumpy Space Prince is chased out of Lumpy Space and transported into the land of Ooo. There, he meets Fionna and Cake and is impressed by their actions and how they live. After deciding that he wants to be like them, his monster parents, who are now bigger and more powerful, return to attack him and his friends. In the end, the prince successfully defeats them after discovering that ignorance is the only solution to defeat parents disapproval.
Lumpy Space Prince appears identical to Lumpy Space Princess, except with a mustache and a darker shade of purple. Like Lumpy Space Princess, he does not have a crown, but the star on his forehead probably indicates his position of royalty. His "Handsome Face" will allow any female who looks at him to become entranced. He does not use his power intentionally, for he is looking for someone exactly like him, such as Lumpy Space Princess.
- Not counting a technicality with Neptr, the only princes shown in the series are Lumpy Space Prince, Prince Gumball, Muscle Prince, Prince Huge, the Box Prince, Turtle Prince and Flame Prince.
- Lumpy Space Prince's voice is almost identical to Lumpy Space Princess', as both of them are voiced by Pendleton Ward.
- In "The Prince Who Wanted Everything," he was voiced by Peter Serafinowciz due to Lumpy Space Princess preventing Ice King from using her voice for him; this voice had a British accent rather than a Valley Girl accent.
- Lumpy Space Prince appears in Adventure Time Battle Party as an alternate outfit for Lumpy Space Princess.
- Interestingly, choosing the Lumpy Space Prince outfit will not actually change Lumpy Space Princess's in-game appearance. Instead, it will only change her voice.
- Lumpy Space Prince's "freaky clothes" were inspired by the Gundam series character, Char Aznable.
- Lumpy Space Prince is a playable character in These Lumps.
- His Mustache resembles Tiffany's.