There's a new Art of Diablo book releasing just after Blizzcon next week, on November 3rd, and not only does the new book confirm that Diablo 4 is in development, it even contains artwork from the game.
According to German publication Game Star, the book will contain artwork from all four games in the series. This seems reaffirmed by a tweet which leaks one of the pages of the book, as you can see below.
The page suggests that Lillith, the Queen of the Succubi will be returning to the series, previously seen in Diablo 2. The page reads that Lilith's debut in Diablo IV is a reimagining of her form that is far different from her previous appearance" - and there's even some new concept art featured in the tweet above.
Of course, none of this is officially confirmed and could very well be an elaborate fake, but we'll soon know for sure when the book releases next week, and likely there'll be official details revealed at Blizzcon too should all this prove true.
Stay tuned to GameFront for any further updates and coverage from Blizzcon.