Hearthstone: Heroes of Warcraft has topped 50 million players, Blizzard Entertainment announced in a press release. The collectible card game hits that milestone just ahead of the launch of its latest expansion, Whispers of the Old Gods.

In February, Blizzard confirmed on a call to investors that more than 40 million people were playing the Mac, Windows PC and mobile free-to-play game. Last May, the company celebrated reaching 30 million registered Hearthstone accounts.

Since its 2014 release, Hearthstone has grown its fanbase thanks to weekly events, regular updates and a thriving esports scene. Blizzard has worked closely with community members to institute some of the game's major changes.

Today's release of Whispers of the Old Gods brings its own major changes, promising to shake up some of the game's most popular cards. Watch our resident Hearthstone experts Phil and Griffin, also known as "the Stonerz," explain the differences below. After that, find out how you can grab some free cards for your Hearthstone deck.