Two years ago, a bonus mission in Sniper Elite V2 lets players intercept a Berlin-bound train and put a bullet in Hitler's head, deviating from the real world event where the Third Reich leader killed himself in an underground bunker. Apparently, that headshot from Sniper Elite V2 didn't take. When Sniper Elite 3 comes out on July 1, you'll get the chance to kill Hitler ahead of schedule all over again.
Just like the 2012 extra, the Hunt the Grey Wolf mission is a pre-order incentive that will unlock when you put money down on the game in advance. The description from publisher 505 Games:
Hitler, Allied code name "Grey Wolf", and his double have embarked upon a clandestine trip to the Libyan port town of Tobruk in 1942. In order to prepare for this mission, and that crucial final shot, you must infiltrate the ancient streets and crumbling rooftops of the German-held town using stealth and distraction. Featuring an expansive open environment, and randomised target identities, journals and locations, no two playthroughs will be the same. The question is — can you tell fact from fiction, the real target from the double?
At this point, 505 should just make a game where you shoot Hitler in different parts of the body as much as you want.