Blizzard started to develop Diablo 4 to be released in the following years.

Diablo is a role-playing game made by Blizzard Entertainment. The first game of the series Diablo was  released on December 31, 1996 and sold over 2.5 million copies around the world. The last game of the series on 2012, Diablo III is 24.8 million copies sold worldwide. Which is massive for the gaming world. The series is compiled of of 3 main games so far and the 6-years of silence will break with the mobile game announcement.

Diablo 4 announcement was reportedly pulled from BlizzCon to rumors

Kotaku announced and discussed this new game and reported: Blizzard’s Team 3 would do two things. The developers, who needed something to work on now that Hades was no more, put together downloadable content for Diablo III called Rise of the Necromancer, a character class add-on that the team hoped would satiate fans who were desperate for more Diablo. And some of them started working on a project code-named Fenris.”

Blizzard looks like want to introduce the new Diablo game on E3 2019.