Very sorry to hear this.  Know what it feels like. Sorry so late to the thread. They are members of the family. They look to us to take care of them. The best thing you could have done for Kitty Jr. is give him a good life and a loving home, which it sounds like you did.

I have heard it said that animals and pets have shorter lives than we do and that this is a helpful training for things that are really important. Not sure that I said it quite right, but hopefully the thought comes across.