This means that you can make the true Ashbringer... When the expansion comes out. ~ Blizzard

This was part of a post that Blizzard put up on its forums before E3, however, just recently deleted it hoping many wouldn't notice or remember... lucky thing though, I did!

I remember most of it:

With the Corrupted Ashbringer Equipped, if you go ANYWHERE near an Argant Dawn NPC they yell something, set your rep at hated, and beat the crap out of you. Now, going to the prince in DM yields nothing, however, going to Scarlet Monestary...

Upon entering the Cathedral instance, Mograine yells something, and all the NPC's become friendly. You talk to Mograine, and his father appears (the same guy that you kill to get the sword). A conversation ensues, and Highlord Mograine The Ashbringer kills his son and leaves, along with the rest of the scarlet crusaders.

However, remember the undead guy locked in the back?

Well, talk to him, he tells you how Highlord Mograine the Ashbringer fell, and how the Argant Dawn was created. When asked if the sword can be cleansed, he says no. However, it can be used to recreate the ashbringer.

His last words tell you to look for the other son... in Outland.

No wonder they tried to hide it!