Princess Anne will escort the Queen's coffin as the late monarch is flown back to London and returns to Buckingham Palace for the last time.
Members of the public are already queueing for the Queen's lying in state at Westminster Hall, which opens on Wednesday, and thousands are still placing floral tributes in Green Park.
At 6pm, the Queen will depart Scotland for the last time. Her coffin will be flown from Edinburgh Airport to London on an RAF Globemaster C-17 flight, accompanied by her daughter the Princess Royal.
The King will be joined by Camilla as he receives his mother's coffin at Buckingham Palace, where she spent so many of her decades as sovereign.
Prince William and the Princess of Wales will also be at Buckingham Palace as a guard of honour if formed.
King Charles and Camilla, Queen Consort, will also tour Northern Ireland today as part of his Operation Spring Tide tour around the UK.
It comes as Brits have flocked to pay their respects to the Queen as her coffin passed through the streets of Scotland before arriving at St Giles’ Cathedral in Edinburgh and on Tuesday evening it will be flown to London.
The Queen’s coffin began its final journey when it left Balmoral on Sunday and after travelling by hearse it is now resting in St Giles’ Cathedral for 24 hours.
People queued for hours to say their goodbyes at the cathedral to Queen Elizabeth, the UK’s longest-serving monarch,
They spoke of their sadness and a sense of peace within the cathedral.
"It was very beautiful, very peaceful and quiet," said Marie Claire Cross, 55, who works in the National Health Service and had been queuing since 11am to enter the cathedral, before finally making it in over seven hours later.
"I was awed by the fact that I was in the cathedral with Queen Elizabeth, who I have looked up to all my life. It was awesome in the true sense of the word and it was so sad."
Television footage showed people filing slowly past the coffin, which was draped in the Royal Standard of Scotland flag and topped with a wreath of white flowers and the Crown of Scotland, historically used for the coronations of monarchs of Scotland.
Some stopped to bow as they passed, others wiped away tears.
Here is Tuesday's full schedule for the mourning of the Queen and the King’s duties that will see him travel from Scotland to Northern Ireland.
Queen’s coffin lies in state at St Giles' Cathedral
The public can pay their respects at the Edinburgh cathedral through the night and until 5pm on Tuesday.
Procession of the Queen's coffin
A hearse carrying the Queen's coffin will leave the cathedral at 5pm, bound for Edinburgh Airport.
At 6pm, it departs Edinburgh on an RAF Globemaster C-17 flight, accompanied by the Princess Royal and her husband, Vice Admiral Sir Tim Laurence.
Its arrival in RAF Northolt in west London is scheduled for 6.55pm and from there will then be transported on a state hearse, accompanied by Anne and Vice-Admiral Sir Tim, to Buckingham Palace.
Its route will be via the A40, Eastbourne Terrace, Lancaster Gate, Bayswater Road, Marble Arch, Park Lane, Hyde Park Corner and Constitution Hill.
Waiting to receive the coffin at the Palace will be the King and the Queen Consort. The Prince and Princess of Wales will also be present.
A guard of honour formed of three officers and 96 soldiers from The King's Guard will be mounted in the Palace Quadrangle.
The Queen's coffin will rest in the Bow Room overnight and details about the route for the lying-in-state queue will be provided late on Tuesday.
The King's duties
The King and Queen Consort will earlier leave the Palace of Holyroodhouse to fly to Belfast as part of Operation Spring Tide - Charles' tour around the UK's home countries.
At Hillsborough Castle, Charles and Camilla will view an exhibition of pictures, showing the Queen in Northern Ireland.
The King will then meet Northern Ireland Secretary Chris Heaton-Harris and party leaders, and receive a message of condolence led by the Speaker of the Northern Ireland Assembly and make a reply.
Charles and Camilla will attend St Anne's Cathedral for a service of prayer and reflection.
They are expected to be greeted by thousands of members of the public, who have been encouraged to line the streets of the city in the afternoon.
The royal cavalcade will travel through Wellington Place, Donegall Square North, Chichester Street and Victoria Street.
And the King and Queen Consort will then undertake a walkabout at Writers' Square, before leaving Northern Ireland.
