'Dragonborn' will see players travel to Solstheim, an island known for its snowy climate and mines, located east of Skyrim.
It's also set to feature dragon riding and new armour types, including Bomemold, Chitin, Nordic and Stalhrim types.
The discovery was made by Bethesda forum members searching files inside the latest patch of the PC version.
Two DLC packs - 'Dawnguard' and 'Hearthfire' - have been released for the game on Xbox 360 and PC, but have yet to arrive on PS3.
Bethesda has previously updated Skyrim to provide improved kill cameras and to add Kinect support to the Xbox 360 version.
The Elder Scrolls V: Skyrim was released for PC, PlayStation 3 and Xbox 360 in November. It was named as the fastest-selling PC game on digital distribution service Steam.
> Read our review of Elder Scrolls V: Skyrim
> Read Digital Spy's 'Dawnguard' review
> Read Digital Spy's 'Hearthfire' review
Watch a trailer for Elder Scrolls V: Skyrim below: