I thought this was an interesting recollection from the late Sir Edward Ford (such a nice man by all accounts), the Queen's former assistant private secretary.
It was Ford who broke the news of George VI's death to both Queen Mary and Winston Churchill. Half a century on, he recalled: "The king's body had been discovered that morning by his valet, in his bedroom at Sandringham. We had a codeword for this eventuality, which was 'Hyde Park Gardens'. The king's private secretary telephoned me and said simply 'Hyde Park Gardens, tell Queen Mary and the prime minister.' The codeword meant that the king was dead, but I knew no more.
"It was 9.15 in the morning and I found Churchill in bed, with Foreign Office papers strewn all round. I said, 'Prime minister, I've got bad news for you. The king died last night.' 'Bad news, the worst,' Churchill replied. He slumped as a man in shock, clearly deeply affected. He then thrust his papers aside, saying, 'How unimportant these matters seem.' I then had to tell Queen Mary. 'What a shock,' she said to me. 'What a shock'."