Harry claimed in his memoir, which is set to hit shelves Tuesday, January 10, that Charles seemingly enjoyed taking jabs at the red-headed prince about his parentage.
"Pa liked telling stories, and this was one of the best in his repertoire. He’d always end with a burst of philosophizing … Who knows if I’m really the Prince of Wales? Who knows if I’m even your real father?" Harry penned in one segment of his book.
“He'd laugh and laugh, though it was a remarkably unfunny joke, given the rumor circulating just then that my actual father was one of Mummy’s former lovers: Major James Hewitt," continued Harry. "One cause of this rumor was Major Hewitt’s flaming ginger hair, but another cause was sadism."
Harry — who shares son Archie, 3, and daughter Lilibet, 1, with Meghan Markle — added that tabloid readers loved the idea that Charles was not actually his father to make them feel better about their own mundane lives.
"Never mind that my mother didn’t meet Major Hewitt until long after I was born," Harry pointed out.
Harry accusing his dad of finding pleasure in making these hurtful remarks was only one of the many bombshells dropped in his upcoming tell-all, in which he also breaks his silence on his stepmother and strained relationship with Prince William.
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Meanwhile, Diana's former partner — who wrote a book about their controversial affair — addressed rumors that he was Harry's father years ago, saying in 2002: "I have been aware for a while that the issue of Harry's paternity has been a major talking point."
"There really is no possibility whatsoever that I am Harry's father," James further pointed out, per People. "I can understand the interest, but Harry was already walking by the time my relationship with Diana began."
Harry was born on September 15, 1984. Diana and the former cavalry officer in the British Army reportedly did not meet until 1986.
"Admittedly the red hair is similar to mine and people say we look alike," James added at the time. "Looking at the pictures I would say he is a much more handsome chap than I ever was."
Page Six obtained an excerpt from Spare.