• Royal biographer Andrew Morton said Prince Harry's memoir is already finished
  • Morton predicted that Prince Charles will be "looking for a hard hat" after the publication of his son's book
  • The Duke of Sussex announced his memoir in July, confirming it will be released in late 2022

Prince Charles likely won't be happy with what Prince Harry would say about him in his son's upcoming memoir, a royal expert has suggested.

Royal biographer Andrew Morton, author of "Diana: In Pursuit of Love" and "Meghan: A Hollywood Princess," told Us Weekly Tuesday that Prince Harry's memoir is already finished.

"If I was Prince Charles, I’d be looking for a pile of coats to hide under," Morton claimed of the upcoming book's potential content. "I think we’re going to see Charles once more in the firing line."

Morton also predicted that the 72-year-old heir to the British throne will be "looking for a hard hat" after the publication of his son's book.

"The thing about Harry is that if you ask him a straight question, he’ll give you a straight answer," added the author of "Meghan and the Unmasking of the Monarchy," which was recently re-released with additional chapters.

Prince Harry announced his memoir in July, confirming in a press release that it will hit bookshelves late next year.

"I'm writing this not as the prince I was born but as the man I have become," the Duke of Sussex said in a statement at the time. "I'm deeply grateful for the opportunity to share what I’ve learned over the course of my life so far and excited for people to read a firsthand account of my life that’s accurate and wholly truthful."

Prince Harry hasn't commented further on what his book might contain. However, the press release from his publisher, Penguin Random House, described it as "the definitive account of the experiences, adventures, losses and life lessons that have helped shape" the prince's life.

Despite the potential drama the book might cause, Morton suggested that Prince Harry's mother, Princess Diana, would have been "thrilled" by the way her son and Meghan Markle have handled themselves since quitting royal duties last year.

"[Princess Diana] would be doing cartwheels," the royal expert told Us Weekly. "She’d be thrilled. Seeing that Harry has made himself and Meghan independent humanitarians irrespective of what the palace might say, she would have applauded that."

Prince Harry seemingly criticized his father's parenting during his and Markle's interview with Oprah Winfrey for a CBS special that aired in March. According to the prince, he was disappointed when Prince Charles "stopped taking" his calls after he revealed his plans to step down as a working royal.

"I feel really let down, because he’s been through something similar. He knows what pain feels like, and Archie’s his grandson," Prince Harry said at the time. "I will always love him, but there’s a lot of hurt that’s happened. And I will continue to make it one of my priorities to try and heal that relationship."

Prince Harry also said that his dad cut him off financially after he and his wife made their royal exit. According to the Duke of Sussex, they wouldn't have been able to make the transition to the U.S. without the money the late Princess of Wales left for him.

"It’s like she saw it coming and she’s been with us through this whole process," he said, adding, "The Netflixes and Spotifys of it all was never part of the plan."

Prince Charles and Prince Harry
Pictured: Prince Harry and Prince Charles laugh during the Invictus Games Opening Ceremony on Sept. 10, 2014 in London. Getty Images/Chris Jackson