The site's trailer features the caption "death, at last, shall spread its wings over all," with the site's HTML showing Diablo 3 and Reaper of Souls trademarks. The quote is also printed in the original Diablo font.
Blizzard has confirmed that it will be holding a press conference at Gamescom on Wednesday August 21.
Yesterday, Blizzard filed a trademark for "The Down Below," with many speculating that it would be the title of a Diablo III expansion.
An invitation sent by Blizzard to media last month said "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."
Blizzard Entertainment president and co-founder Mike Morhaime has also said the company's Gamescom announcement would be Diablo-related.
Gamescom will run from August 21 to August 25 in Cologne, Germany.