According to a trailer shown at the Gamescom opening night live event, Return to Monkey Island will be released on September 19th, which is International Talk Like a Pirate Day. The game will be available on two platforms.
Gilbert first teased the game this year in what appeared to be an April fools joke, but a few days later it turned out that he wasn't kidding. The new game is a direct follow-up to The Secret of Monkey Island and Monkey Island 2: Le Chuck's Revenge, though, in an interview with The Verge, Gilbert and Dave Grossman said the game could include canon from other games in the series.
The free set of horse armor will be given to those who pre-order the game. The trailer states that the horse armor has no use in the game.