Queen Elizabeth II, the UK's longest-serving monarch, has died at Balmoral aged 96, after reigning for 70 years.
Her family gathered at her Scottish estate after concerns grew about her health earlier on Thursday.
In a statement, Buckingham Palace said: "The Queen died peacefully at Balmoral this afternoon.
"The King and the Queen Consort will remain at Balmoral this evening and will return to London tomorrow."
All the Queen's children travelled to Balmoral, near Aberdeen, after doctors placed the Queen under medical supervision.
What happens next?
A well-organised set of arrangements, dubbed 'Operation London Bridge', after the death of Queen Elizabeth II has been underway since the 1960s.
According to a publication by the Independent, a code word has been set up to deliver the news of her death to the government.
Queen Elizabeth II's death will be signalled by the word “London Bridge is down”.
The words will signify the monarch has passed away and kick off Operation London Bridge
According to The Guardian, the Prime Minister at the time will be woken, if not already awake, and informed by civil servants that “London Bridge is down”
The Foreign Office’s Global Response Centre will immediately inform 15 governments outside the UK where the Queen is also the head of state.
The centre will then inform the other 36 other nations of the Commonwealth for whom the Queen has served.
The news will then spread to the public and the media.
A footman in mourning clothes will be sent out of the door at Buckingham Palace at the same time to pin a notice of the news to the gates.
The official palace website will feature her news on just one page under dark background.
According to the Independent, Sky News and ITN, which have reportedly spent years rehearsing the death of the Queen by substituting the monarch's name for “Mrs Robinson”, the family will contact royal experts who have already signed contracts to speak exclusively to them.
An alert will be sent out to commercial radio stations to switch on blue 'obit lights' for the inoffensive music to be played.
