The 4th class has been recently announced at BlizzCon. It is the monk.
The man seemed ignorant of the cold. He was dressed like a beggar, wearing little more than an orange sheet wound around his body, leaving half of his chest exposed. A garland of large wooden beads hung around his thick neck. His head was completely shaved, with the exception of a wild bushy beard. Then, recognition struck me: upon his forehead he had a tattoo of two red dots, one larger than the other. As any informed student of the peoples and cultures of this world must also realize, this man was one of the monks of Ivgorod, the secretive and reclusive holy warriors of the country.
The Monk uses fighting-game like combos and holy magic, favoring speed over toughness. The class will have complementary skills…skills that work together better than they work apart. He will be a tougher character to master, for advanced players.
This monk looks inspired by the more oriental shaolin type instead of the non-canon Hellfire clergy monk. More to look forward to in Diablo III.