User blog comment:Master Sima Yi/Assassinews 03-12-'14 — New Assassin's Creed in Victorian London leaked/@comment-187.38.102.21-20141215011728/@comment-4786308-20141215145331

I think Arno rejoins the assassins after he killed Germain, that's why he is given the Master Assassin's robes. But they could have at least showed it in a cutscene.I'm not sure but I think it's explained in the Unity novel.