family visits

where can I find the etiquette for the way the scenario below should have been handled?

I am a divorced grandfather. My married daughter lives in the same town. My son lives 1000 miles away. Until recently my son and daughter got along OK.

My son had a son out of Wedlock and gets along poorly with the mother of his 11 year old child. The mother and child live 1000 miles away. To the best of my knowledge, my son gets along very well with his son, pays his child support, and visits when possible, a couple of times a year. I contact the grandson on holidays and try to stay in touch with him.

Until the event below, my son and daughter got along OK.

My married daughter, without my knowledge, nor the knowledge or consent of my son, had the grandson and his mother visit her and stay with them for several days in town recently. My son is upset about the matter, and I don't understand it.

Of course, my daughter broke no law in what she had done, but how should this have been handled from an etiquette standpoint?