'You didn't even know her': Prince William and Harry on their confusion over public grief for Diana

The Duke of Cambridge and Prince Harry have spoken of the bewilderment they felt at the public grief following their mother’s death, admitting they had struggled to understand why so many strangers were crying when they “didn’t even know her”.

The Duke, who was 15 when Diana, Princess of Wales, died, said he had felt “a bit protective at times about her” as he walked behind her coffin with his brother, who was just 12.

Admitting the “alien environment” of grieving in the public eye had been among the most difficult moments of his life, the Duke said he had wondered of weeping members of the public: "You didn't even know her, why and how are you so upset?"

He has since come to understand how much the Princess had meant to people, he said, as he and his younger brother speak candidly about how the duty of performing for the watching world in 1997 affected them.

The Duke and Prince Harry spoke as part of a documentary for the BBC, which sees them publicly defend the decision made by the Prince of Wales and the Queen to keep them at Balmoral following the car crash which killed their mother.

It is the first time in a series of high-profile interviews about the Princess’ death that they have praised their father for his part in helping them grieve.

Prince Harry said: "One of the hardest things for a parent to have to do is to tell your children that your other parent has died.

"How you deal with that I don't know but, you know, he was there for us.

"He was the one out of two left and he tried to do his best and to make sure we were protected and looked after.

"But, you know, he was going through the same grieving process as well."

The Duke also paid tribute to the Queen’s decision to keep her grandsons at Balmoral in the days following her death on August 31, 1997.

Then, she weathered heavy criticism from the public who accused the Royal family of keeping the children “prisoner” away from the people.

The Duke said: “I don’t think anyone, even my grandmother, had seen this anything like this before. I think all of use were on new territory.

“But for Harry and I, my grandmother and father believed we were better served at Balmoral, having the walks and the space and peace to be with the family and not be immersed having to deal with serious decision or worries straight away.

“I think it was a very hard decision for my grandmother to make. She felt very torn between being a grandmother to William and Harry, and her Queen role.”

Saying he was thankful there had been no smartphones to keep them up-to-date with what was happening in London, he added: “We had the privacy to mourn and collect our thoughts, and have that space.”

Lady Sarah McCorquodale, Diana’s sister, added of the Queen’s decision: “She did absolutely the right thing. If I was her I would have done that.”

In contrast to the peace of Balmoral, the streets of London were lined with members of the public overcome with emotion and demanding sight of the senior members of the Royal Family.

The weight of expectation placed on the young Princes required them to put on a “game face” in order to avoid “completely and utterly breaking down”, said the Duke.

Prince Harry added he had not cried in public at the time and was probably still unable to, explaining: “Whatever happened then has changed me in that sense.”

Describing coming back to London to meet the public, the Duke said: “What was very peculiar but obviously incredibly touching was everybody crying.

“The wailing and the crying and people wanting to touch us… I was 15 and Harry was 12. It was like nothing you can really describe, it was very unusual.

“They were shouting and literally wailing at us. Throwing flowers, yelling, sobbing, breaking down, people fainted, collapsed.”

Speaking of the funeral procession, he added: "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.

"I did feel a bit protective at times about her. I was like, 'you didn’t even know her'. Why and how are you so upset?

"Now looking back, over the last few years I’ve learned to understand what it was she gave the world and a lot of people.”

Prince Harry added: “The way that people were grabbing us and pulling us into their arms… I don’t blame anybody for that, of course I don’t, but it was those moments that were quite shocking.”

In hindsight, he said, he was “really glad” he had walked behind the Princess’ coffin, saying he had come through a phase of wishing his Royal status away to devote himself to duty and “making her [Diana] proud”.

The Duke added: “When you have something so traumatic as the death of your mother when you’re 15, it will either make or break you. I wouldn’t let it break it, I wanted it to make me.”

The programme, Diana, 7 Days, will be broadcast on Sunday, August 27th at 7.30pm on BBC One.