Spoiler. Don't watch if you don't want to see what goes down when you defeat him.
http://www.youtube.com/watch?v=bJ0EJTeQ5gw&feature=player_embedded
Video taken down by Blizzard. Pwnd.
[spoiler]Arthas: omg i'm finally dead
Terenas: lol dude ur goin to hell
Arthas: omg plz no
Tirion: lol
Bolvar: lol tirion
Tirion: wtf arent you dead
Bolvar: no u tard im the lich king
Tirion: ur my hero
Bolvar: i cant be ur hero, dun tell nobody bout me, i has to control the skerg to make sure they behave
Tirion: plz?
Bolvar: no, our secret
Tirion: :([/spoiler]
Reminds me of the ending to Terminator: Salvation.
"[spoiler]This is John Conner. Nothing's changed...[/spoiler]"