After his mother's death, Prince Harry asked his father a heartbreaking question.

Prince Harry was just 12 years old when he woke to the news on Sunday, August 31, 1997, that his mother had been killed in a car accident in Paris.

Her death was so unprecedented, so shocking, that the royal family was unprepared for how to deal with such a tragedy. Their initial reaction was to “do as they had always done”.

According to biographer Tina Brown, in a documentary that aired in the UK last night detailing the days after Diana’s death, the “everything is normal” attitude confused young Harry so much, he asked his father if his mum had really died.

"Prince Harry actually asked his father, 'Is it true that Mummy's dead?'" Brown said in the Diana: 7 Days That Shook The Windsors documentary.

"The children couldn't understand why everything was as normal, except a couple of hours earlier they'd been told their mother had died."

Upon learning of Diana's death, Prince Charles and the Queen decided to let the boys sleep and not wake them with the news.

The same day, Prince Harry and his older brother William - then 15 - attended church as normal. But there was no mention of Princess Diana during the service at Crathie Kirk church.

The Queen had requested no referenced be made to her death, for fear any mention of her would be "heartbreaking" and too upsetting for the young boys.

The Queen reportedly ordered all TV and radios to be hidden at Balmoral so they couldn't hear the details of how their mother had died.

Royal biographer Ingrid Seward recalled the public was confused by seeing the boys going about their normal routine just hours after their mother's death.

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"The first thing we saw of the boys was when they were going to church for Sunday service," he told the program.

"And people were saying, 'How could they? These boys have just lost their mother.'"

The documentary also alleged there were tensions between Charles and his mother over his decision to fly to Paris to collect her body.

After their divorce, Diana had been stripped of her 'Her Royal Highness' title, but Charles convinced his mother to lend him the royal private plane.

"The irony is Charles fought for Diana, more than he'd ever fought for her in her lifetime. He really did," The Daily Mail's Richard Kay said.