The recent announcement of The Definitive Experience of Metal Gear Solid V has made some question if the mysterious Mission 51 would be included. The mission’s boss battle and some cut scenes were included in the collectors edition of the game but the mission itself was absent, with some fans suggestion it held the “real” ending to the game.
“Mission 51 is not complete, its development was cancelled prior to the initial release of The Phantom Pain,” tweeted Konami. “Mission 51 is additional story content that was cancelled before development finished, but its definitely not the ending.”
“I’m afraid we have no current plans to further develop for Mission 51,” they added. The also point out that the story of certain characters in the game is continued in the other titles in the series, but with MGSV’s timeline occurring before the orginal Metal Gear Solid, so players may have forgotten that.
Source: Metal Gear Informer