William and Harry walked side-by-side behind their father
All viewing areas for the procession were full, London's City Hall said
The Queen will lie in state for four days ahead of her funeral on Monday
The King has travelled more than 1,500 miles around the UK in his first week on the throne
US President Joe Biden called the King on Wednesday to offer his condolences on the death of his mother
Pulled on a gun carriage of The King’s Troop Royal Horse Artillery past silent crowds, the oak coffin was draped with a Royal Standard and adorned with the priceless, glittering Imperial State Crown.
Thousands of mourners flocked to see the moving sight of the Queen departing the official residence where she spent so much of her working life at the heart of the nation, with viewing areas declared full ahead of the procession starting.
The King walked in line with the Princess Royal, the Duke of York and the Earl of Wessex.
Behind the quartet were the Queen’s grandsons in a line – Peter Phillips, the Duke of Sussex and the Prince of Wales.
In bright summer sunshine, funeral marches played by military bands added to the solemn mood that left some mourners weeping, while others held up their camera phones to record the historic moment.
The Queen’s coffin was transported on the George Gun Carriage, which carried King George VI’s coffin from Sandringham Church to Wolferton Station in February 1952 and was used during the funeral of the Queen Mother in 2002.
During the service at Westminster Hall, the senior royals stood in formation facing the coffin on its purple-covered catafalque, which was flanked with a tall, yellow flickering candle at each corner of the wide scarlet platform.
The Duchess of Sussex appeared to take a deep breath as the Queen’s coffin passed in front of her.
Cries of “God save the King” could be heard as the King and the Queen Consort left.
Shortly after the arrival of the coffin at Westminster Hall, US President Joe Biden said he had spoken to the King on Wednesday to offer his condolences and shared the “great admiration of the American people” for the Queen.
Four officers from the Household Cavalry – two from the Life Guards and two from the Blues and Royals – began the first six-hour vigil around the coffin, taking their places at the corner of the catafalque.
Mourners have already joined the queue to attend the Queen’s lying in state, which continues until 6.30am on Monday, the day of the Queen’s state funeral.
As of 5.20pm on Monday, a live tracker run by the Department for Digital, Culture, Media and Sport showed the queue was around 2.9 miles long, stretching as far as London Bridge.
Government guidance warns that mourners joining the queue will need to stand for “many hours, possibly overnight” and with very little opportunity to sit down.