Various reports are saying we could very well be seeing a new Overwatch character on Monday. IGN says It all started with a French movie theater who is screening the new animated short that debuts this Monday. In their advertisement, they mentioned the "discovery of new heroes" (they have since said this is a typo, but we know how that goes).
Then Neogaf user Nirolak started mentioning references voice files found in game to a character named Sombra, and here we are. So don't be surprised Monday if we get an announcement of new characters for Overwatch because it definitely looks like that's going to be happening! Watch out for the new animated short premiering at 10 am PST this Monday!