Prince William and Prince Harry at Queen's Procession Echoes Heartbreaking Walk at Diana's Funeral

As they followed in procession a coffin that carried their grandmother Queen Elizabeth through London on Wednesday, Prince William and Prince Harry walked a similar path to the one they took 25 years ago for the funeral of their mother, Princess Diana.

On September 6, 1997, William and Harry — then ages 15 and 12, respectively — followed a route that began at Kensington Palace, Diana's London home, to Westminster Abbey.

"It was one of the hardest things I've ever done, that walk," William said in the 2017 BBC documentary Diana, 7 Days. "It felt like she was almost walking along beside us to get us through it."

In the same film, Prince Harry recalled hearing people screaming in the crowds that lined the London streets. "The broadcast news today still talks about the silence and of course there was a huge amount of silence, but what I remember is every 50 yards or whatever certain people in the crowd just unable to contain their emotion," he said. "That was a big thing."

JEFF J. MITCHELL/AFP/Getty From left: Prince Philip, Prince William, Charles Spencer, Prince Harry and Prince Charles walk behind Princess Diana's casket at her 1997 funeral

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Bells tolled continuously then, as they did on Wednesday as the princes accompanied their father, King Charles III, and other members of the royal family on the procession of Queen Elizabeth's crown-topped coffin from Buckingham Palace to Westminster Hall, where the late monarch, who died September 8 at age 96, will lie in state until Monday morning.

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A mourner and member of the British public Jo Cadzow tells PEOPLE she had Diana's sons on her mind as she watched the procession for the Queen. "I thought of those two men," she said. "It must bring back memories for them 25 years [ago]. I have huge respect for them doing it."

Chris Jackson/Getty Images Prince William and Prince Harry

The decision to have William and Harry follow their mother's coffin through the streets of London in 1997 was not made easily.

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Diana's brother, Charles, 9th Earl Spencer, said in an interview with BBC Radio 4 20 years later that it was "cruel" to make the young princes walk behind the coffin and that he was against the plans.

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"It was the most horrifying half an hour of my life," Spencer said. "It was just ghastly. … It was the worst part of the day by a considerable margin, walking behind, well, my sister's body, with two boys who were obviously massively grieving their mother. And it was this sort of bizarre circumstance where we told you had to look straight ahead. But the feeling, the sort of crashing tidal wave of grief coming at you as you went down this sort of tunnel of deep emotion, it was really harrowing, actually, and I still have nightmares about it now."

JUSTIN TALLIS/POOL/AFP via Getty Images

But friends of the royal family have said that it was William and Harry's grandfather, Prince Philip, who told the young princes, "If I do it, will you?"

"It was a collective family decision," William confirmed in the 2017 documentary. "But we were overwhelmed by how many people turned out, it was just incredible. There was that balance between duty and family, and that's what we had to do."

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DANIEL LEAL/POOL/AFP via Getty Images King Charles, Prince William and Prince Harry

Harry also recalled it being a "group decision" to have them follow Diana's coffin on its journey through London.

"Before I knew it, I found myself with a suit on with a black tie and a white shirt, I think, and I was part of it," he said "Genuinely, I don't have an opinion on whether that was right or wrong. I am glad I was part of it. Looking back on it now, I am very glad I was part of it."

William added that at the time, "I couldn't understand why everyone wanted to cry as loud as they did and show such emotion as they did, when they didn't really know our mother."

Getty Prince William, Princess Diana and Prince Harry

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"Now, looking back," he continued, "I've learned to understand what it was that she gave the world, what she gave a lot of people."

Cadzow, who lives in Warminster, said she was pleased to see members of the royal family process behind Queen Elizabeth's coffin on Wednesday.

"It was very good to see the family behind their mother and grandmother," she tells PEOPLE. "And so moving to see Her Majesty's coffin and to be able to have the opportunity to say goodbye and thank her for 70 years."