I was in boy mode when I took my son to a birthday party for one of my nieces today (the one I've mentioned before, who has met me as Alice).
Last night, my son and I made a birthday card for her. At my son's insistence, the card was from 4 names, my son, my wife, my male name and "Alice".
My 3 nieces all loved it. My 12yo nephew looked a little confused and asked "who is Alice?" I answered, do you remember the photo your sister used to have on her wall before she moved out of home? He still looked a little confused and my niece said "you know, the one you thought was aunty ***."
He knew the photo we were talking about but still didn't get it. "But who is she?" My niece just said "a family friend" and left it at that. I later told her that I describe my alternate identity as my "identical twin" brother or sister, depending on which I am at the time. :)
He was the only one of my immediate relatives who I wasn't sure whether he knew or not. All of the rest do. Now that his 3 sisters know that he doesn't know, I suspect that he'll know fairly soon. :)