One of his best:
"Can you tell the difference between them?"
- The Duke's question after President Barack Obama said he met with the leaders of the UK, China and Russia.

Also:
Kenya's independence ceremony in 1963 when Philip represented Britain. As the Union Jack was about to be hauled down, he turned to Kenyan independence leader Jomo Kenyatta and asked: "Are you sure you want to go through with this?"

And:
He asked a Scottish driving instructor in Oban: "How do you keep the natives off the booze long enough to pass the test?"

Edited by hedgehog50 (05 May 2017 3.55pm)

We have now sunk to a depth at which the restatement of the obvious is the first duty of intelligent men. [Orwell]