There is major point raised by this discussion.
This point seems to be still raised for royals, but not anymore for commun people.
I explain myself. There are two major theories still applied. Jus soli and jus sanguinis. What could define your ethnicity and nationality? Where are you born and live or what is the origin of your family? And if the second applies how far behind can you go?
What about the Americans and Australian? Are they still only English or French or whatever was the homeland of the first who arrived there? I think the have the right to be just American or Australians with different origins.
Now for royals. DoE was a mixture. Yes the Danish had a German origin, nevertheless I doubt if the actual DRF would be happy to be called still German. Same for the Belgian RF.
Prince Philip comes from queen Olga, so Russian, with German mixture also.
Only a genetiste and genealogist could write down and find the percentage if his blood per origin. But the question is, how far behind you can go. All royal families were taking foreign brides, and are a huge mixture, but there is a stage the blood definition stops and the ground raised and feelings are predominant.
Can you say that BRF are still German, and Swedish still French?
Considering the special conditions he had in his life, I doubt DoE that he migh feel Greek and of course not German. If he had to feel one country, he was feeling British. Of course this is my only opinion.
I'm saying that nationality and ethnicity isn't as simple as you suggest it is. Nationality isn't set in stone and the concept of nationality is a fairly modern one that can't be imposed on societies pre-dating the creation of this concept. In many European countries it's not uncommon for families to change nationality and ethnicity within generations and then back again. Just because someone came from Germany 600 years ago doesn't make their descendants German today. Even if they mostly married other Germans this doesn't necessarily make their descendants German today if they chose not to be.
Philip's ancestors in the male line have ruled in Scandinavia for 600 years and before that in the female line for 600 more years and most of them (there are some very poignant exceptions) considered themselves Scandinavian in spite of what languages they spoke (Norse, Danish, German, French - most of them grew up speaking several like Philip himself did) and where their mothers were born.
Is Philip of predominantly German descent? Yes.
Does this automatically make him German? No.