Camilla will now become Her majesty the Queen Consort.
Yesterday (8 September), the tragic news was announced that Queen Elizabeth II had died at her home in Balmoral.
Following her death, Charles immediately became King, going by the title King Charles III, while his wife Camilla became the Queen Consort.
The move was announced by Queen Elizabeth II herself in February this year, on the eve of the 70th anniversary of her Accession.
In a statement at the time, she said: "I would like to express my thanks to you all for your support.
"I remain eternally grateful for, and humbled by, the loyalty and affection that you continue to give me.
"And 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."
Elizabeth's late husband Philip, however, was never known as King during her reign.
This was because rules dictate that the husband of a ruling Queen is to be known as Prince Consort, with the title of King reserved for royals who inherit the throne and then reign.
Buckingham Palace had previously sent out a statement yesterday afternoon announcing that Her Majesty had been placed under medical supervision following concerns over her health.
"Following further evaluation this morning, the Queen’s doctors are concerned for Her Majesty’s health and have recommended she remain under medical supervision," it read.
"The Queen remains comfortable and at Balmoral."
Clarence House said The Prince of Wales and the Duchess of Cornwall, as well as the Duke of Cambridge had travelled to Balmoral to be with her.
The death of the Queen is a monumental moment in the country's history.
Having ascended to the throne in 1952, aged just 27, she is the longest reigning British monarch, and the second longest reigning monarch in the world.
Earlier this year, she marked the incredible milestone of 70 years on the throne, becoming the first British monarch to celebrate a Platinum Jubilee, with the country enjoying a huge celebration in her honour.
Under her reign, she witnessed a list of historic moments, including the Troubles and the signing of the Good Friday Agreement.
She also lived through the UK joining the European Union and subsequently leaving it in 2016.
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