QuoteToday in 1953 Queen Mary, The Queen's grandmother, died peacefully in her sleep. She was 85 years old. At 11:15pm an announcement was posted outside Marlborough House announcing her death. According to The Yorkshire Post from 25 March 1953: "While sleeping peacefully, Queen Mary died at twenty minutes past ten o'clock."
More: History Rewind: Queen Mary dies after illness | Royal Central (http://www.royalcentral.co.uk/blogs/history/history-rewind-queen-mary-24738)
It's very interesting to read about the protocol surrounding the announcement if her death and the worsening of her condition. I hope when the current Queen passes, it won't be announced via Twitter.