By Michael Holden and Humza Jilani
LONDON (Reuters) -Prince William has told how walking behind his grandmother's coffin brought back challenging memories, alluding to the death of his mother, as mourners from all walks of life queued for hours on Thursday to file past the late monarch's coffin.
The new heir to the throne told well-wishers that the military procession had "brought back a few memories", a nod to the day 25 years ago when, as a boy of 15, he had followed the casket of his mother Princess Diana to her funeral.
The death of Queen Elizabeth, Britain's longest-reigning monarch, has prompted an outpouring of emotion across the country. Tens of thousands have queued for hours, including through the night, to file past her coffin and pay their respects to the 96-year-old.
Presidents, prime ministers and royalty from around the world will gather on Monday for the state funeral for Elizabeth, queen for 70 years whose global stature was almost without equal.
The official in charge of the huge ceremonial event said on Thursday that he hoped the funeral would unite people from across the globe.
Ending 10 days of national mourning, Elizabeth will finally be laid to rest at a chapel at her Windsor Castle home alongside her husband of 73 years Prince Philip, who died last year.
The body of the late queen is now lying in state in London's Westminster Hall.
"The queen held a unique and timeless position in all our lives," said the Earl Marshal, Edward Fitzalan-Howard, the Duke of Norfolk, England's most senior peer who is in charge of state occasions. "It is our aim and belief that the state funeral and events of the next few days will unite people across the globe."
As he spoke, the queue to see the queen's coffin stretched more than 4.5 miles (7.24 km) along the south bank of the River Thames, past landmarks including Tower Bridge, crossing Lambeth Bridge as it neared Westminster Hall.
The estimated queuing time is at least eight hours.
Officials expect about 750,000 people to view the coffin before the lying in state ends at 6.30 a.m. (0530 GMT) on Monday.
On Wednesday William walked in a solemn procession with his younger brother Harry and father, King Charles, as the coffin was taken from Buckingham Palace to the Palace of Westminster.
It was a scene reminiscent of when, William and Harry, then aged 12, followed Diana's casket when it was taken on a similar procession through central London.
"The walk yesterday was challenging ... brought back a few memories," William said as he and his wife Kate spoke to well-wishers and viewed the sea of floral tributes outside the royal Sandringham estate.
Charles, who has returned to his Highgrove home in southwest England after a hectic schedule of events since Elizabeth's death last Thursday, and his three siblings, Princess Anne and Princes Andrew and Edward, will hold a silent vigil alongside the catafalque on Friday evening.
Some of those queuing to see the coffin had travelled from abroad, dropping off bags at nearby hotels to join those moving slowly through Westminster Hall. There were former soldiers with military medals and babies being carried by their parents. Many wiped away tears.
The mourners included former Prime Minister Theresa May and her husband Philip, who bowed their heads before the coffin as they filed past with members of the public.
Amy Tsai, 24, said she had travelled from Taiwan in May and had taken part in celebrations for the queen's jubilee in June in the Scottish capital Edinburgh.
"Now I'm waiting in line to see her lying in state. I'm just shocked," she said.
For the first time, palace officials also provided details of the funeral, likely to be one of the grandest ceremonies ever seen in the British capital, involving thousands from the military and with details overseen by the monarch before her death.
"It was her majesty the queen that went through the plans and made sure they were alright and the king is implementing those plans," a spokesman for Charles said.
After the lying in state ends early on Monday, the coffin will be carried onto the State Gun Carriage of the Royal Navy where 142 naval service personnel will pull it to Westminster Abbey, the same church where Elizabeth was crowned in 1953.
The funeral service will begin at 11 a.m. (1000 GMT) and last about an hour. At its conclusion the Last Post will sound and there will be a two-minute silence to be observed by the nation.
The body will then be taken on the gun carriage in a large procession, with Charles and other royals walking behind, to the Wellington Arch at Hyde Park Corner. Guns will fire and parliament's Big Ben bell will toll every minute.
The state hearse will then convey the coffin to Windsor Castle where there will be a further procession before a service at the castle's St George's Chapel.
In a later private ceremony, Elizabeth will be buried with Philip at the King George VI Memorial Chapel where her parents and sister, Princess Margaret, were also laid to rest.
Buckingham Palace said it would not provide a list of those who will attend the funeral but royalty, presidents and other world leaders are expected, although certain nations, including Russia, Afghanistan, and Syria, were not invited.
Charles will hold an official state event on Sunday to meet the dignitaries who attend. On Thursday he spoke to several world leaders including the president of Germany and the king of Saudi Arabia. The White House said he spoke with U.S. President Joe Biden on Wednesday.
Asked how the new monarch was bearing up, his spokesman replied: "I think people who've worked with the king know just how resilient and hardworking he is."
Elizabeth's body was brought to London on Tuesday from Scotland where it had remained since her death last week at her summer home Balmoral Castle.
Her coffin now lies in Westminster Hall on a purple catafalque placed on a red platform. It was covered by the Royal Standard flag and topped with the Imperial State Crown placed on a cushion, alongside a wreath of flowers.
Soldiers and 'Beefeaters' - the red-coated warders who usually guard the Tower of London - stand vigil. At one point on Thursday, Britain's defence secretary, Ben Wallace, took his place standing guard in front of the coffin.
(Reporting by Humza Jilani, Estelle Shirbon, Farouq Suleiman, Alistair Smout, Angus MacSwan, William James, Kate Holton, Kylie MacLellan and Elizabeth Piper, Editing by Janet Lawrence, William Maclean and Daniel Wallis)