Details on the zombie mode of the upcoming video game "Call of Duty WWII" are set to be revealed on July 20, according to a teaser posted by game developer Sledgehammer Games' head Glen Schofield.

Schofield tweeted a photo of an undead creature, along with a date. This came a month after developers revealed some intriguing information about the game -- zombies are back and they are based on real life.

The company's founders Schofield and Michael Condrey recently told Edge Magazine via Reddit that the zombies are actually based on real events. "There's some really authentic stuff in there," Schofield said, adding, "There's back story that's based on real events."

The addition of zombies has been a recurring feature in previous titles in the "Call of Duty" franchise. These undead walkers previously appeared in 2008's "Call of Duty: World at War" and continued in the 2010 release "Call of Duty: Black Ops," as well as in a number of spin-off games.

Fans and critics alike will be very interested to see how the developers integrate the war against zombies in the backdrop of the second world war, around which the game's main story revolves. It would also be interesting if this new story that they will introduce with the upcoming game is going to be maintained and pursued in the zombie modes of future installments of the successful first-person shooter franchise.

Ahead of its release, the company also announced that the title will also feature some gameplay changes, including the removal of health regeneration in the campaign. "You have to worry about every bullet," Schofield told Polygon, adding, "You're not the superhero. You can't just stand there taking seven bullets, ducking, shooting again. It's refreshing for us to deal with recruits who aren't Tier One warriors, to show that vulnerability. They're naïve. It's been a really cool challenge creating this different kind of gameplay."

"Call of Duty: WWII" is an upcoming first-person shooter video game developed by Sledgehammer Games, and published by Activision for PlayStation 4, Xbox One and Microsoft Windows. The game is slated for a worldwide release on Nov. 3.