The news comes from an invitation sent to media today that reads, "We're making a special announcement that's sure to capture the attention of the Heavens, Burning Hells, and all the shadowed places that lie between."
The event itself will take place on the first day of Gamescom, August 21, at 11:30 a.m. local time.
Gamescom takes place August 21-25 in Cologne, Germany.
GameSpot will be on-hand at the event.
Blizzard Entertainment has a number of projects in the pipeline, including Diablo III for consoles, Blizzard All-Stars, Hearthstone: Heroes of Warcraft, StarCraft II: Legacy of the Void, and a next-generation MMO, in addition to continued support for World of Warcraft.