This mount was released in Patch 3.1.0 as part of the new world event, the Argent Tournament. It can be purchased from the tournament quartermaster for 150 , the currency for the tournament. Mount Purchase Requires=150 Champion's Seals earned from completing the different parts of the Argent Tournament. More Info on Champion's Seal=  In-Game Images=   Check Them Out! Argent Hippogryph= In-Game Images=  Check it Out!
Patches and hotfixes