ladybirder; It was/is very distressing, we had just an hour before been watching him/her, the first time seen on its own, trying to figure out how to reach the food which the more acrobatic parent had been giving it. I went in and got a fat ball and hung it at a more accessible place in the lilac tree. We went indoors and shortly after there was a bang and it was all over, - really gutted. I think the parents wouldn't know it had happened and the book says they have 3 to 7 eggs so there may be others I hope.
Most of the windows to the back garden have silhouette hawks fixed to them, but this one didn't, I've now made a temporary one in black paper, but too late.