Latest Hearthstone expansion slated for release in mid August (no specific date as always), will bring 135 new cards to the game. You can pre-purchase 50 packs and get the Frostmourne cardback as well.

Highlight of this expansion will be the addition of the ‘Death Knight’. Each class gets a new legendary ‘Hero Card’ that transforms them into a Death Knight, complete with a different hero power and other effects.

https://www.youtube-nocookie.com/embed/DgaBjPyMtXo?rel=0

(via)