The confirmation came during a special announcement kicking off Hearthstone's Americas Winter Championship tournament. Blizzard unveiled a cinematic trailer for the expansion (featured above). The developer announced that it will contain 134 new cards themed around the old gods, a collection of evil eldritch beings of incredible power from Warcraft lore.
Whispers of the Old Gods will launch some time in late April or early May of 2016. An early patch to prepare for the expansion will debut this coming Monday, March 14, which will introduce the new deck recipes feature.
You can find more details on the new expansion in our reveal feature here.