Blizzard has officially announced Diablo 3: Reaper of Souls, the first expansion pack for last year's hit action-RPG.

Described as a "darker expansion", Reaper of Souls introduces a new character class - The Crusader - and increases the level cap to 70. It also focuses on new villain Malthael, the Angel of Death, and his legion of Death Angels, the Reavers.

"In Malthael's eyes, humans are demonic and they must be destroyed," Blizzard explained at its Gamescom press conference.

The Crusader is a new mid-range melee character that Blizzard refers to as a "tank in human form". The character is able to use its armour as part of its weaponry, with Crusader Shields acting as a "core part" of the character's weapons. The Crusader also has access to mid-range spells.

Each existing character class will receive additional skills, too.

New monsters have also been promised for Reaper of Souls alongside a new city, Westmarch, referred to as "the gothic power of the west".

Diablo 3's loot system has been tweaked for Reaper of Souls, too, with what Blizzard calls 'Loot 2.0'.

The new system introduces 'Smart Drops', which drops weapons and items better suited for your character class, and drops Legendary weapons more often.

Blizzard says that the new system will help "make sure that playing the game is the most fun, rewarding way to [earn loot]."

A new Artisan lets players 'Transmogrify' and 'Enchant' their rare and legendary items as well, to help players get "exactly what they want" from their loot.

"From the beginning, Diablo has always been about the struggle between good and evil, and Reaper of Souls explores the darker notes of that conflict," said Mike Morhaime, CEO and cofounder of Blizzard Entertainment. "This expansion also represents a big milestone in the ongoing evolution of Diablo III, with key enhancements to the core gameplay, along with a new act to experience, a powerful new character class, tons of new loot, and even more end-game options. We think players will love playing Reaper of Souls, and we can't wait to get it into their hands."

A release date for Reaper of Souls has yet to be announced. For the first screenshots, head through to our image gallery.