A period of national mourning has officially begun across the country and will continue until the the day of the Queen's state funeral, the government has said.
The announcement comes as the UK grieves the death of Queen Elizabeth II, the country's longest-serving monarch.
A period of royal mourning will be observed - by members of the Royal Family, royal household staff and representatives, together with troops committed to ceremonial duties - from now until seven days after the Queen's funeral, the date of which will be confirmed in due course, Buckingham Palace said.
Senior members of the Royal Family spent the night at Balmoral following the 96-year-old monarch's death, including the King and Queen Consort, and the next in line to the throne, Prince William.
His brother Prince Harry, was the first to leave the Royal Family's Scottish residence this morning for Aberdeen International Airport, where he boarded a British Airways flight to London.
In the capital, 96 rounds of gun salutes - one for every year of the Queen's life - will be fired in tribute to the late monarch from 1pm in Hyde Park by The King's Troop Royal Horse Artillery and at the Tower of London by the Honourable Artillery Company.
A service of prayer and reflection will be held at St Paul's Cathedral in central London at 6pm.
Around 2,000 seats will be allocated to the public on a first come first served basis.
What will be taking place today to mark Her Majesty's death?
King Charles III and the Queen Consort will return to London from Balmoral later, with the monarch due to hold his first audience with Prime Minister Liz Truss.
The House of Commons sitting will not start at 9.30am as planned, with both Houses of Parliament due to gather at noon instead.
MPs and peers will be invited to pay tribute to the Queen in the session, led by Ms Truss, which is set to last until 10pm.
The government is not expected to announce any other business, unless anything urgent occurs, to allow focus to fall entirely on the Queen during the 10-hour sitting.
Ms Truss and senior ministers will also attend the public service of remembrance at St Paul's Cathedral.
The government is then due to confirm the length of national mourning, which is likely to be around 12 days, from now up to the day after the Queen's funeral.
It will also announce that the funeral day will be a public holiday in the form of a day of national mourning.
Throughout the course of Friday, King Charles is likely to meet the Earl Marshal - the Duke of Norfolk - who is in charge of the Queen's funeral, to approve the carefully choreographed schedule for the coming days.
He will also be preparing to address the nation in a televised speech, where he will pay tribute to his mother and pledge to serve as head of state, the details of which are expected to be announced later today.
As tributes flood in from around the globe, hailing the Queen's unwavering commitment to serving her country and the Commonwealth, books of condolences are being placed in town halls and large screens set up in major city centres for people to follow rolling news coverage.
There are no physical books of condolence at the royal residences, all of which will remain closed until after the Queen's funeral. But there is an online book of condolence for those who wish to leave messages.
Churches have been urged to toll their bells, with the Church of England sending out guidance to parishes, chapels and cathedrals across the country encouraging them to open for prayer or special services.
The Central Council of Church Bell Ringers has recommended tolling muffled bells for one hour from noon.
Bells will ring out at Westminster Abbey, St Paul's Cathedral and Windsor Castle.
What will happen on Saturday?
Unusually, the House of Commons will hold a sitting on Saturday to allow senior MPs to take the oath of allegiance to King Charles III.
This will begin at 2pm and will be followed by tributes, which will continue until 10pm.
The session will end with a "formal humble address" to the King at the end, "expressing the deep sympathy of the House" on the Queen's death, the House of Commons said in a statement.
All MPs will have the option to take the oath to the King when the House returns, but are not obliged to.
Commons Speaker Sir Lindsay Hoyle will determine the timetable for the following days, but it is expected to be significantly reduced until after the state funeral as Parliament adjourns.
This means new laws cannot be passed until Parliament returns, though it could be recalled for the most pressing matters.
Also on Saturday morning, an Accession Council will meet at St James's Palace in London to formally proclaim King Charles III as the new sovereign.
The first public proclamation of the new sovereign will then be read in the open air from the Friary Court balcony at St James's Palace by the Garter King of Arms.
Union flags go back up to full-mast at 1pm and remain there for 24 hours to coincide with the proclamations before returning to half-mast.