I once sang for the Queen... Well almost. We were supposed to sing for the Queen when she was here in 2002 with Prince Philip (for memory it was the opening of the Roma St Parklands although I could be wrong) but it started raining so instead they played a recording of "God Save the Queen" and "Advance Australia Fair". But I was there, and I still saw her, so I'm counting it. I'm pretty dull otherwise.
ETA it was actually for CHOGM now that I think about it. But I'm sure it was just after the Roma St Parklands opened which is why I thought that was it.