Amazing story about a WW2 encounter over Germany - and battlefield morality

Someone started cutting onions next to me when I read the inscription the German wrote in a book he sent the American:

"In 1940, I lost my only brother as a night fighter.

On the 20th of December, 4 days before Christmas, I had the chance to save a B-17 from her destruction, a plane so badly damaged it was a wonder that she was still flying.

The pilot, Charlie Brown, is for me, as precious as my brother was.

Thanks Charlie.

Your Brother,
Franz"