Over the weekend, Blizzard rolled out a series of announcements, including new Overwatch characters, at BlizzCon 2018. They also took some time to talk about an upcoming game in the Diablo franchise, but it wasn't quite what most fans were expecting. Diablo Immortal, a mobile spin-off, was met with a lukewarm reception, but it sounds like a much more tantalizing reveal is in the works.
Shortly after the event, Kotaku's Jason Schreier reported that Blizzard is actively developing Diablo 4 and that they've already recorded an announcement video featuring Blizzard co-founder Allen Adham. Schreier initially claimed that Blizzard had planned to air the video during BlizzCon, but changed their minds and pulled it. However, Blizzard disputes this report, claiming that there were no plans for any such reveal at BlizzCon.
"First off we want to mention that we definitely hear our community. We generally don't comment on rumors or speculation, but we can say that we didn't pull any announcements from BlizzCon this year or have plans for other announcements. We do continue to have different teams working on multiple unannounced Diablo projects, and we look forward to announcing when the time is right." — Blizzard
While Blizzard denies that any game reveal was pulled from Blizzcon, they don't outright dispute the claim that the video exists. Schreier and his sources (two people "familiar with Blizzard's plans") are still confident that the video already exists and will release at some point in the future.
One source has since suggested to Schreier that Blizzard was not yet ready to reveal the game, as the game has undergone massive changes during four years of development. Diablo 4 has reportedly existed in at least two different iterations with different directors. As such, it's unclear exactly when they'll feel comfortable revealing details to the public.