Prince William was among the royals who walked behind Her Majesty's casket as it left Buckingham Palace to lie in state in Westminster on Wednesday.
He stood shoulder-to-shoulder with his brother Prince Harry as the pair joined King Charles and other senior members of the family.
While viewing flower tributes to the Queen in Sandringham on Thursday, William reportedly chatted to an onlooker and told her the procession brought back memories of when he was a teenager, the Telegraph reported.
Jane Wells, 54, from Lincolnshire, told the newspaper: “He said how difficult it was yesterday and how it reminded him of his mum’s funeral... Catherine said it’s just been such a difficult time for all of them, for the whole family.”
He was also caught on camera talking to the public, was heard saying: "Doing the walk yesterday was challenging, it brought back a few memories.
"It's kind of one of those moments where you think to yourself 'I've prepared myself for this, but I'm not that prepared'."
William and Harry were positioned behind their father as part of the procession, which left the palace at 2.22pm, through the streets of London.
The pair walked behind the coffin of their mother Diana, Princess of Wales almost exactly 25 years ago, when they were just 15 and 12.
He previously said doing it was the "hardest thing" and was a "very long, lonely walk."
Speaking of the balance between personal and public life, he added there was conflict "between me being Prince William and having to do my bit, versus the private William who just wanted to go into a room and cry, who'd lost his mother."
During Wednesday's procession, the Queen's coffin was draped with a Royal Standard and adorned with the priceless, glittering Imperial State Crown as it was pulled on a gun carriage of The King’s Troop Royal Horse Artillery.
In bright summer sunshine, funeral marches played by military bands added to the sombre mood that left some mourners weeping, while others held up their camera phones.
The journey from the palace to the ancient Westminster Hall, where King Charles I was tried for treason in 1649, took 38 minutes – passing landmarks the Queen knew well like Horse Guards Parade, the Cenotaph and Downing Street.
Accompanied by her family, the solemn occasion marked the point at which the Queen was effectively being handed over to the the nation for her lying in state, over four days ahead of the state funeral on Monday.
William stared straight ahead as he processed directly behind his father the King, in keeping with his place as the new heir to the throne.