The royal historian researched both Prince William and Prince Harry as part of his upcoming book about the two Dukes titled Battle of Brothers. Now, Mr Lacey has provided insight into the brothers’ sometimes tumultuous disagreements.
Regarding William in particular, the author has claimed Camilla, Duchess of Cornwall, had said to her friends: ‘That boy’s got a temper.’
The Duke would allegedly “unleash” anger at his father, shocking his step-mother at the time.
The author has stressed the two royals have now mended their relationship and “have grown much closer together”.
Mr Lacey said: “Their father-son spats are said to be episodes in the past.”
However, he suggests the relationship between the Duke of Cambridge and the Prince of Wales was at times rocky in the past.
On one occasion, the author claims the prince “flatly refused” to give “some sort of nod” to his father during an ITV documentary about their late mother Princess Diana.
Mr Lacey made his observations on William’s temper in the Daily Mail, which has serialised excerpts of the book ahead of its publication on October 15.
Other snippets from the book focus more on the relationship between Prince Harry, Duke of Sussex, and Prince William.
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It is possible the meeting between the Queen and Harry was less tense, as the author also reports the monarch “had always had a soft spot” for the Duke of Sussex.
Her Majesty was also “delighted” when Meghan Markle was introduced to the Royal Family.
In addition, the author has said the Duke and Duchess of Sussex nearly moved to Africa following their plans for a royal departure.
The plan has been described as a sort of compromise which would have given the Sussexes “both honour and responsibility” due to a British Commonwealth of Nations role.
At the same time, it could have allowed the couple to live a more “ordinary” life.
However, the African plan did not end up materialising. Harry and Meghan currently live in Santa Barbara, California.
The couple signed a deal with video streaming service Netflix in recent weeks, which will see them produce their own content for the platform.
They also signed up to the high-profile Harry Walker public speaking agency.