Amid the many revelations in Prince Harry's bombshell book, Spare, is a surprising tale of how he holed himself up in a Norfolk hotel room while on a training exercise which saw him call in RAF fighter jets for a dummy bombing raid on Prince Charles.
The Duke of Sussex recounts how, before his tour in Afghanistan's Helmand Province, he chose to train in the county instead of the army's usual training areas, to keep his pending deployment a secret.
At the time, in 2007, the then 23-year-old Harry was serving as a reconnaissance troop leader in the Household Cavalry.
When he needed to become combat-ready, by learning to control different kinds of aircraft operating over the battlefield, as a forward air controller, he chose Sandringham.
"The last place anyone would think of Prince Harry getting himself combat ready," he writes in Spare, which was published this week. "Granny's country estate."
The cloak and dagger mission saw him check in incognito to Knights Hill Hotel, on the outskirts of King's Lynn, in a "hundred quid" room, where "the privacy was thrilling".
From there, he headed out on the nearby marshes on a quad bike to co-ordinate RAF fighter jets overhead.
He says his father, the then Prince Charles was staying at Sandringham, as his training began.
"Then one day he looked up in the sky and saw a Typhoon aircraft doing low passes along the seawall and he figured it must be me," he writes. "So he got in his Audi and hurried over.
"He found me on the marshes, on a quad bike, talking to a Typhoon some miles off."
Harry says his father was impressed by how hard he was working in his new role.
"He particularly loved seeing me steer those jets over the marshy flats at ungodly speeds," he adds in the book.
"I mentioned that the good citizens of Wolferton didn't share his enthusiasm. A 10,000-kilo jet roaring just over their tiled roofs didn't exactly cause jubilation.
"RAF Marham had received dozens of complaints. Sandringham was supposed to be a no-fly zone. All complainants were told: Such is war."
Harry says as his father left him to his work, the heir to the throne became an unwitting participant in the wargame.
"As he went down the track, I told the Typhoon: New target. Grey Audi. Headed south-east from my position down track towards a big silver barn.
"The Typhoon tracked Pa, did a low pass straight over him, almost shattering the windows of his Audi.
"But ultimately I spared him. On my orders."
Spare details Prince Harry's military career along with a childhood dominated by the death of his mother Diana, Princess of Wales, in a car crash in 1997.
It also chronicles his romance and marriage to Meghan Markle and subsequent estrangement from his family.
Spare, by Prince Harry. Penguin Random House, £28.
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