vSully1,297,489 Locked 31 Aug 2014 21 Sep 2014
Story related and cannot be missed.
This achievement will unlock after defeating Malthael, talking to Tyrael, and then choosing to end the game and return to the menus.
Note that you must have progressed through all of the quests in Act V, so this achievement will NOT unlock if you join a friends game and simply kill Malthael.