Haru-ōji
The title of this article is conjectural; an official name for the article's subject has not been found, so it has been given a fitting title by the editors. If an official name is found, then the article should be moved to its appropriate title.
The Prince of the Mushroom Kingdom is, as the name says, the prince of the Mushroom Kingdom. He appears in the anime movie: "The Great Mission to Save Princess Peach".
He first appears in the begining of the movie as a blue dog who has been turned into a dog by King Bowser. At the end, thanks to Mario and Luigi, the prince is turned back into a human.
The prince is most likely Princess Peach's brother. He has never appeared in any Mario game, or even been mentioned. Plus, Peach has never mentinoed a brother in the games, and probably does'nt even have one.