Hearthstone cinematic trailer screenshot
Screenshot of Hearthstone's Whispers of the Old Gods Cinematic TrailerScreenshot/Blizzard

Blizzard Entertainment has announced that its popular collectible card game Hearthstone: Heroes of Warcraft has topped 50 million players. The digital card game hit the milestone just ahead of the launch of its third full-sized expansion, Whispers of the Old Gods.

In February, the developer confirmed that more than 40 million fans were playing Hearthstone on Mac, Windows PC and mobile in a call to investors. Last May, it stated that game had 30 million registered accounts.

Based on the World of Warcraft universe, the latest Old Gods expansion is now live, bringing massive changes to the game including new cards and significant changes to its competitive play. The expansion introduces 134 new cards to the game including legendary Old Gods C'Thun, Yogg-Saron, N'Zoth and Y'Shaarj as well as "corrupted" versions of some old favourites.

Hearthstone also has two primary game modes – Standard and Wild. In the "Standard" mode, only the original set of Hearthstone cards and the previous two expansions may be used. The "Wild" mode allows players to use any card, but could potentially mean a much more limited pool of opponents and longer wait times between matches as well.

"Whispers of the Old Gods adds an exciting new set of creepy, corrupted cards to Hearthstone," Mike Morhaime, CEO and cofounder of Blizzard Entertainment, said in a statement. "We can't wait to see how creative players are with the ancient evil of the Old Gods in their hands."

Players opening their first pack of Whispers of the Old Gods will receive the legendary Old God C'Thun and two Beckoner of Evil cards. In celebration of the launch, anyone who logs in to Heartstone will also receive three Whispers of the Old Gods card packs for free. Two new one-time Quests are available to complete in succession as well. Players who win two games in Standard mode will be rewarded with five packs of Whispers of the Old Gods. Winning seven games in Standard mode will give you five more packs.

Since its release in 2014, the addictive digital card game has risen in popularity due to its regular updates, weekly events and flourishing eSports scene. According to SuperData Research, Hearthstone is the top game in the $1.2bn (£823m) digital card-battling market, generating about $20m per month despite being free-to-play, thanks to its in-game purchases.

Hearthstone: Whispers of the Old Gods was released in North America on 26 April and arrived in Europe and Asia on 27 April.