Prince Harry said his father appeared "like a ghost" to tell him his mother Princess Diana had died.
Harry described laying in bed during the harrowing night when the dreadful news was broken to him, after his brother William had already been informed.
In the sleepy moments before being overcome with tiredness, Harry describes seeing his father appear in his bedroom, writing: "He was standing by the bed, looking down. His white coat made him look like a ghost in a play.
"He gave me a half smile and looked away. The room was no longer dark. There was no light either. It was a strange gloom, almost brownish, almost like the water in the old bathtub.
"He looked at me in a strange way, with an expression I had never seen before. With fear."
Harry goes in to explain how his father described his mother's accident, with Harry assuming she was injured but would recover.
Charles, Harry claims, told his "dear son" about "complication" and his Diana had suffered "head injuries" before Harry began begging his father while repeating the word "no".
Harry claims his father got up and passed through another room, saying he kew he had "already told Willy".
However, the book reportedly says that Charles did not physically comfort his son and that Harry says he "felt like a politician" as he later met grieving Brits.
Harry was at the royals' Balmoral estate with his father and brother Prince William when they were given the life-changing news about their mother.
Prince Harry also claims that King Charles would later joke "who knows if I'm even your real father?" during rumours that the Duke of Sussex was the son of Princess Diana and her ex-lover Major James Hewitt.
In his new tell-all book, Spare, Prince Harry delves into his past while discussing his mother Diana's affair with Major Hewitt.
The Duke of Sussex reportedly mentions in the memoir that his dad was fond of anecdotes and that one of his stories included a visit to a mental asylum where he met a man claiming to be the Prince of Wales - a role that the King had at the time of the visit.
According to Prince Harry's recount of the story, Charles wagged his finger at the patient and said he was the only Prince of Wales.
Harry adds that his dad had a tendency for ending his stories with a "philosophical flash" and in this instance Charles mused about whether anyone could be sure they were not the mentally ill one themselves, "living in a fantasy".
Prince Harry then claims in the book that Charles joked: "Who knows if I'm even your real father? Perhaps your father really is in Broadmoor, my dear son!"
