William and Kate viewed floral tributes left by the public outside Sandringham Estate, the queen's Norfolk retreat, where she and family members regularly spent time, including a decades-long tradition of gathering there for Christmas.
A reporter on the scene who spoke to a woman who met William Thursday said the prince told her the death of his grandmother brought back memories of the death of his mother, Diana, the Princess of Wales.
William and his brother Prince Harry walked in a procession behind Diana's coffin after her death on Aug. 31, 1997, following a car crash in Paris.
On Wednesday, almost exactly 25 years later, William and Harry walked in a procession behind the queen's coffin as it was moved from Buckingham Palace to Westminster Hall.
"He told us yesterday had been particularly difficult and following the coffin had reminded him of his mother’s funeral, of Diana," said Jane Wells, who had come to lay flowers for the queen at Sandringham. “He said it had been very difficult.”
Wells continued, "I said, 'Your mother would be so proud of you and thank you for sharing your grief with us,' and he said, ‘I’m learning that she was everyone’s grandmother, the way people have reacted.'"
Another person in the crowd told William she was close to tears, to which he replied, according to reports, “Don’t cry now. You’ll start me.”
William and Kate viewed an overflowing tribute of flowers for the queen outside the gates of Sandringham, which is located close to their own country home, Anmer Hall, where they spend down time as a family with their three children, Princes George and Louis and Princess Charlotte.
Kate is believed to have worn to Norfolk a pair of diamond and pearl drop earrings that belonged to the queen.
Norfolk is located around 100 miles from Windsor, England, where William and Kate now have their primary home on the grounds of Windsor Castle, where the queen also spent much of her time during her 70-year reign.
In the 24 hours since the queen's coffin was moved from Buckingham Palace to Westminster Hall, thousands of people have lined up in London to pay their respects to Britain's longest-reigning monarch.
The queen's coffin will lie in state at Westminster Hall until her funeral on Sept. 19, at Westminster Abbey.
Tributes like those William and Kate viewed at Sandringham have grown across the U.K. in the week since the queen's death.
The queen's daughter Anne, the Princess Royal, traveled to Glasgow, Scotland, to view tributes left to the queen and to meet with representatives of organizations of which the queen was patron.
Anne traveled with her mother's coffin earlier this week on its journey from Balmoral Castle in Scotland, where the queen died, to London.
Prince Edward, the queen's youngest child, and his wife Sophie, the Countess of Wessex, spent time Thursday in Manchester, England, where they viewed tributes left at St. Ann's Square and met with community members.
Members of the royal family and invited guests will gather on Monday for a final goodbye to the queen.
Her state funeral is scheduled to begin at 11 a.m. local time Monday at Westminster Abbey, making the queen the first sovereign to have a funeral there since 1760.