In September of last year, Andy Cosby (Hellboy animated series) inadvertently leaked news of a Diablo animated series for Netflix for which he would be the showrunner. Since then, there has been tons of Diablo-related news, but nothing more has been said about the series. However, a new Diablo trademark registration has popped up that reads, "Downloadable films and movies featuring narratives based on a video game and provided via a video-on-demand service".
The application was filed by Blizzard Entertainment on March 8, 2019.
Andy Cosby further fueled rumors with a cryptic tweet a few days later about a "super secret project" that further adds to the speculation.
It's killing me that I can't talk openly about my new super secret project, because my new super secret project is just so frikkin' cool! Soon... very soon...— Andy Cosby (@andycosby) March 14, 2019
Hopefully, we'll learn more soon.