Assuming that you are not, indeed, the current incumbent of the British Throne (otherwise, gosh, greetings, Your Majesty. :-)), I agree, but that doesn't mean that the image is not under copyright; indeed, the image is almost certainly under copyright, as PD works are rare outside of the United States for things newer than the 1920s.
Dude was born in 1879. This photo might well have been taken before 1923 and gods know under what copyright laws. British? Even if it was taken between 1923 and 1935 the photographer might well have died before 1935, which would put the photo in the public domain under European laws.
And if the angry guy with the website really held a license for the picture he'd probably state its source and author somewhere and not just froth at the mouth when asked.
He probably feels he *owns* the picture since he scanned it in or some such.
Anyway, I agree, this... 'individual' seems to be quite taken with invective about other's attitude to 'his' website. Perhaps he feels that his content has already been "stolen" (eurgh, it's intellectual property; it cannot be stolen unless the creator no longer has access to it) by us in some way, and is so very affronted? I cannot imagine that anyone would fly off the handle quite so much at the simple instigation of a request for permission...
He maintains one of the few decent websources on what is a relatively obscure subject. Like other people in the same position he will find himself used extensively by Wikipedia as a source. This is probably the cause of his fury.
Regards, Haukur