The Princess Royal had warned Coronation organisers that a feather, which made global headlines on the day after obscuring Prince Harry’s face, was “quite a decent-sized hat” – but was told to wear it anyway.

The Princess raised concerns about the large headpiece, she has said, and had only changed seats to one in front of her nephew at the last minute, seeking a “speedy exit”.

The plume of the Blues and Royals caused amusement worldwide for blocking Prince Harry’s view from his third-row seat at his father’s Coronation.

A new book, Charles III: New King. New Court. The Inside Story, by Robert Hardman, sees the Princess defend herself against allegations she had done it on purpose.

“At the Coronation itself, Prince Harry was seated in the third row of the royal section, immediately behind Princess Anne, who was wearing a striking red-plumed bicorn hat that remained on her head throughout,” he writes.

“Social media snipers instantly concluded that Harry had been deliberately placed behind his aunt’s tall hat to obscure his view.

“This is nonsense. Not only do the Lord Chamberlain’s Office not think like that, but the Princess Royal had only switched to that seat after her request for a speedy exit.

”‘The hat was an interesting question,’ the Princess recalled later. ‘I said: ‘Are you sure you want me to keep the hat on? Because it’s quite a decent-sized hat.’ And the answer was yes. There you go. Not my choice.’”

Prince Harry had attended the Coronation without his wife and two children, who remained at home in California.

He made only a brief appearance in public, taking the first possible flight after the ceremony to make it home to see Archie Mountbatten-Windsor on his fourth birthday.

The seating plan had relegated him to the third row, where he took a position between Jack Brooksband, the husband of Princess Eugenie, and the late Queen’s cousin Princess Alexandra.

Social media had been alight with jokes about the red feather, with critics of the Duke of Sussex claiming she had worn it on purpose to cement his estranged status.

The Duke had been seen in pleasant conversation with his aunt beforehand, also talking to Princess Beatrice’s husband, Edoardo Mapelli Mozzi, during the service.

There was no known interaction with his brother and sister-in-law, the Prince and Princess of Wales.

Writing in his own memoir Spare, Prince Harry relayed how it was Princess Anne who was first to greet him at Balmoral after the death of Elizabeth II, when he arrived later than most of his family.

Meeting him with a hug, she took him to the late Queen’s bedroom to pay his respects.

The book, “Charles III: New King. New Court. The Inside Story” by Robert Hardman, is out in hardback on January 18, published by Macmillan.