Today, Thursday 8 September, it was announced by Buckingham Palace that Her Majesty the Queen had died at the age of 96, following a 70-year reign.
For years, there has been a plan in place in the UK to navigate the aftermath of the Queen's passing, also known as Operation London Bridge.
So what happens next? When does the Prince Charles officially take over and what does this mean for the Duke of Cambridge?
The day of the Queen's death is known as 'D-Day'. After the Queen passed away earlier today, the prime minister was informed by the Queen's private secretary.
There was an 'official notification' alerting the public to news of her passing and the royal family's website has since changed to a black page featuring a statement and image of her Majesty.
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The statement reads: "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. Thursday, 8 September 2022."
Over the following days, the prime minister is expected to schedule an audience with the new monarch - The Prince of Wales - who will then give a broadcast to the nation.
Charles' wife, Camilla, who has been a senior member of the royal family since marrying Prince Charles 17 years ago, will have the title of Queen Consort when Charles officially becomes king.
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The Queen announced the news earlier this year, explaining: “When, in the fullness of time, my son Charles becomes King, I know you will give him and his wife Camilla the same support that you have given me.
“And it is my sincere wish that, when that time comes, Camilla will be known as Queen Consort as she continues her own loyal service.”
It is thought that the new King Charles III will take on a tour of the UK in the days to follow.
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Meanwhile, the Duke of Cambridge will become the next in line to the throne. It is thought he will become the Prince of Wales, taking over from his father. It's not clear whether the Duchess of Cambridge will be given the title of Princess of Wales.
The Queen's funeral has already been agreed to be a Day of National Mourning. The state funeral will be held in Westminster Abbey and a two-minute's silence will take place at midday; all those across the country are expected to take part to pay their respects.
If you have experienced a bereavement and would like to speak with someone in confidence, contact Cruse Bereavement Care via their national helpline on 0808 808 1677
Lucy Devine