And the prize goes to TPC ... the adult just flew out of the nestbox, couldn't stand the harrassment for food I suspect (he had been the one to feed them last) and when they got to the edge of the box, the birds stopped shook out his/her feathers and I could see his/her left foot perfectly - no coloured band, so that would be Ivy ... Princess' coloured band is on her left leg, Ivy's is on his right and both/either would have been clearly visible.
Not sure Princess would have been able to fit in there with four wet and begging kids .... not sure she would have been able to tolerate it either. Ivy seems to be a much more, lets say, laid back kind of male ...