When Anduin was just a child, the Prophet Velen foresaw that he would one day lead an army of Light against the forces of the Void. With the announcement of the Worldsoul Saga, it finally looks like this prophecy might come to pass!
When introducing the Worldsoul Saga, Chris Metzen asked the question, «Will there eventually be an apocalyptic confrontation between the forces of the Light and the Void?» Then, when introducing the War Within Cinematic trailer, he reminded us that
The cinematic shows Thrall speaking to Anduin, who doesn't feel like leading anyone right now. By the end, Anduin promises that he's ready to face whatever's coming — and, as we know from the planned next three expansions, the Void is coming for the soul of our world.
A final confrontation between the Light and the Void is one that has been prophesied for a long time. Over a decade ago, when Anduin was just a child, the Draenei leader — prophet Velen — saw a vision of this confrontation. In it, Anduin led both the Alliance and the Horde against the forces of the darkness.