The next big Metal Gear Solid game is coming out this September, according to an inadvertent video leak on IGN. We'll finally see MGSV: The Phantom Pain on September 1, 2015.
For some context: MGS publisher Konami had partnered up with IGN to hype up the game and promise a big announcement for tomorrow at 9am, but it looks like someone pulled the trigger on IGN's video too early, as discovered by NeoGAF poster Nibel. Whoops. You can watch the video here, until they take it down.
UPDATE (12:23pm): Video's down. WHOOPS. Konami/IGN marketing plans derailed.