Because for six years, that little boy had looked at photographs of Arthur in his uniform and called him Grandpa, and to Arthur that was not a technicality that a DNA test could void.

One Sunday, not long after, Leo looked up at him, uncertain, having overheard enough to be frightened, and asked in a small voice: “Are you still my grandpa?”

And Arthur — a retired colonel, a man of bloodlines and estates and family names — knelt down to look the six-year-old in the eye, and said the sentence I have thought about nearly every day since.

“Biology makes relatives, son,” he said.

“Decisions make family.

I decided a long time ago, and I am not the sort of man who un-decides.