So I was listening to the Soundtrack "Legendary" from patch 5.4 and saw a comment at the bottom that intrigued me. He said the main theme of the track was actually in the "Dark Portal theme". I looked it up and surely he was right.
The theme at :15 in "legendary" is the same theme at :50 in "The Dark portal theme". I cant post the videos yet but go take a look. Its pretty interesting.
The Cinematic Intro movie theme is the one im talking about. Not the login screen.