Be warned, there are incredibly massive spoilers for the end of Icecrown Citadel beyond the cut below, and in the embedded video. We will say no more until you've clicked through. If you don't want to be spoiled, stop reading right now. Seriously!
Update: The video has been removed due to a copyright claim by Blizzard.
Dataminers around the world are rejoicing as the datafiles for tomorrow's patch, patch 3.3.2, are starting to trickle down into our hands. MMO-Champion's Boubouille in particular immediately dug up the cinematic for the Fall of the Lich King, sealing the fate of Arthas and heralding a new king.
The cinematic confirms what many of us have known all along: the identity of the new King of the Damned.