Prince William has revealed for the first time how he felt his mother's presence beside him as he walked behind her coffin on the day of her funeral, at the age of 15.
Opening up about his mother's death in a BBC documentary to mark the 20th anniversary of her passing, he recalled: "It was one of the hardest things I've ever done, that walk. It felt she was almost walking along beside us to get us through it.
His brother Harry, who was 12 when his mother died, remembered being comforted by members of the public whose "hands were wet because of the tears they had just wiped away".
Diana, 7 Days, which will be broadcast on 27th August will feature candid interviews with those who were at the 'eye of the storm' in the days following the princess' death, including her sons and siblings, members of the royal household and former Prime Minister Tony Blair.
The film will examine what was it about the late Princess that provoked such a public outpouring of grief; how the week after her death shaped the country's relationship with the monarchy and how Britain has changed in the 20 years since Diana's death.
Henry Singer singer is the award-winning director behind the documentary, with previous work including Baby P: The Untold Story and The Betrayed Girls, about the Rochdale child grooming scandal.
The documentary is further evidence of Prince William's new openness, as he tries to lead by example in encouraging others to speak up about issues surrounding mental health.
He initially refused to speak publicly about his mother's death but in recent years he's been more open, especially after becoming the patron of Child Bereavement UK.
In a previous interview Prince Harry also opened up about walking behind his mother's coffin and said that with the benefit of hindsight, it should not have happened.
He told Angela Levin in an exclusive interview with Newsweek magazine: "My mother had just died, and I had to walk a long way behind her coffin, surrounded by thousands of people watching me while millions more did on television.
"I don't think any child should be asked to do that, under any circumstances. I don't think it would happen today."
In a recent Channel 5 documentary Diana: 7 Days That Shook The World it was revealed that the team organising her funeral made up of representatives from the royal family, Number 10, the police and Diana's family argued over whether they boys should walk in the procession.
The programme claimed Earl Spencer wanted to walk alone behind Diana's coffin, but Prince Charles was adamant that he should join the procession.
The rest of the funeral team felt William and Harry, then 15 and 12, should be there, too. However, William was refusing to join the procession, saying he wanted to grieve privately, according to Tony Blair's former head of government relations Anji Hunter.
Hoping to persuade William to change his mind, five days before the funeral on September 6, the team set up a telephone conference call with Balmoral via a big loudspeaker box on their conference table.
"I can remember - it sends a tingle up my back, actually," says Hunter. "We were all talking about how William and Harry should be involved and suddenly from this box came Prince Philip's voice.
"We hadn't heard from him before, but he was really anguished.
"It's about the boys," he cried, "They've lost their mother."
"I thought, 'My God, there's a bit of suffering going on up there'."
In fact, it was the Duke of Edinburgh who was the one who persuaded William to walk in the procession right at the eleventh hour on the morning of the funeral.
"He put a grandfatherly arm around him and said 'look, if i come too, will you do it?'," the Daily Mail's Richard Kay explained in the documentary.