Prince Philip was partly educated at Salem in Germany, which would account for the fluency in German.
Otherwise, he seems to have grown up in a mainly English-speaking milieu, though it's good to hear about the French and Greek.
Apparently the Queen also speaks French extremely well. There is a nice story from a few years ago of her making an impromptu broadcast on Quebec radio when a presenter rang Buckingham Palace posing as the then Canadian Prime Minister, Jean Chretien. The listeners were most impressed by her fluent French as well as her command of Quebec politics. Off topic, I know.
Ann