Prince Charles was pressured by his father, Prince Philip, into marrying Princess Diana -- a union that was doomed. 

The claim was made by royal biographer Ingrid Seward, who recently published a book on the Duke of Edinburgh titled, “Prince Philip Revealed: A Man of His Century.”

The British author is the editor-in-chief of Majesty magazine. The 72-year-old has been covering the British royal family since the 1980s and has written more than 20 books on the subject.

On Friday, Seward told Us Weekly that the Prince of Wales, 71, had “felt he’d been pushed into marrying Lady Diana Spencer, a shy nanny and nursery school teacher."

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Prince Charles and Princess Diana divorced in 1996. (AP, File)

“He told some of his friends that he felt pressurized into marrying Diana because Philip said, ‘You’ve either got to marry her or let her go. You can’t string… a young girl [along]. She’s only 19. You can’t string her along,’” said Seward.

“And all the press is saying, ‘Oh, this is going to be the next queen,’” she continued. “‘You’ve got to take a stand and say that this is not going to work, or you marry.”

Seward said Charles, who is next in line to the throne, “was frightened by his father” and proceeded to propose.

“He probably thought, ‘Well, OK. I’ll marry her if that’s what you want me to do,’” said Seward.

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Seward also alleged that before Diana was linked to Charles, there were discussions about her being better suited for Charles’ brother, Prince Andrew

Prince Charles 'was frightened by his father,' Prince Philip, and proceeded to propose, claims royal biographer Ingrid Seward. (Photo by Tim Graham/Getty Images)

Diana married Charles, who was 12 years her senior, in 1981. The royal wedding was famously televised and watched by 15 million people in Britain alone. 

Andrew, the Duke of York, went on to marry Sarah Ferguson in 1986.

“I think some of Diana’s friends thought that Andrew would be more fun for her than Charles, because he was very much her age and he was full of fun and everything else,” Seward told the outlet. “But Diana wasn’t interested in Andrew. It was Charles she was interested in.”

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“She had been around the royal family ever since she was a little girl because her father and her family lived on the Sandringham Estate and her father was what’s called an inquiry to the queen,” Seward shared. “So, he sort of was in the royal household.”

Charles and Diana welcomed sons Prince William in 1982 and Prince Harry in 1984.

Seward also alleged that before Diana was linked to Charles, there were discussions about her being better suited for Charles’ brother, Prince Andrew.  (Photo by Dan Kitwood/Getty Images)

The couple later separated in 1992 and were divorced by 1996. Diana passed away in 1997 at age 36 from injuries she sustained in a car crash.

Charles married his longtime love Camilla, Duchess of Cornwall in 2005.

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Andrew, 60, and Ferguson, 61, welcomed daughters, Princess Beatrice in 1988, and Princess Eugenie in 1990. The former couple divorced in 1996.

Philip, now 99, married Queen Elizabeth II, 94, in 1947 and are still together.

“I’ve always been interested in Philip and he seems a bit of an enigma,” Seward explained on why she chose to explore the royal’s life in her latest book. 

Philip, 99, married Queen Elizabeth II, 94, in 1947 and are still together. (Photo by Hulton Archive/Getty Images)

“He had bits about him, but not a great deal about him,” she shared. “I just knew that he’d always be there in the background. He likes to stay in the background.”

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“If you look at any pictures of him and the queen, you’ll see that he’s always two steps behind,” added Seward. “I’ve met him a lot of times and I thought, ‘You know, he’s someone that’s sort of a bit of an unexplored person.”