Is That Kormac in the Diablo IV Features Trailer?

I'll confess that my only real experience with the Diablo franchise is Diablo III, which I'm given to understand is a more triumphant game than most - the initial game ends with us defeating the Prime Evil and saving the Heavens, and while Tyrael expresses some concern about it, the Nephalem also defeats Malthael, saving the world.

Of course, in order for there to be a plot, things have to go bad.

Where are the Nephalem in all of this? And are the heroes of Diablo III not going to be Nephalem themselves?

I believe Diablo IV is going to be set twenty years after Diablo III (unless it's 40.) I haven't checked the voice actor for the features trailer, but it appears to be an older man who is speaking to a "brother" who died at some point. Like Kormac, the Templar follower who fought alongside us in Diablo III, the narrator has a kind of Northern English accent (I don't think I could tell you the specific one, unfortunately.) Could this be an aged, retired Templar who has lost the strength to fight the evils that plague the world?

Given the way that the earlier games ended, I do worry that the heroes of Diablo III might, in fact, have become villains by the time of Diablo IV. But also, as godlike beings of incredible power, one also wonders what role they're playing in the Diablo cosmos now. Did someone figure out how to kill them? Or have they gone elsewhere?

I know Diablo IV is meant to be a return to the darker tone of the earlier games (not that Diablo III was super bright) but I'm curious to see how the earth-shaking events of Diablo III come into play.