Throw the Shattered Pieces of Val'anyr into Yogg-Saron's maw while he's casting Deafening Roar and defeat Yogg-Saron and recover the Reforged Hammer of Ancient Kings.
This can only be completed in Heroic mode and only if at least one Ulduar Watcher is not assisting you.
The Archivum Console has hinted at a possible way to rebind the fragments of Val'anyr: you must get the fragments inside the physical form of the being known as Yogg-Saron.
It sounds like a long shot, but for an artifact of such power you think the risk might just be worth it.
You will receive:
|Val'anyr, Hammer of Ancient Kings|
You will also receive: