King Charles III was reportedly in great pain after Prince Harry's attacks on his beloved wife Queen Consort Camilla.
Harry's bombshell claims about the Queen forced King Charles to take a stern action against the Duke.
The 75-year-old asked his son and daughter-in-law to leave the royal residence, which was gifted to them by the late Queen Elizabeth II, as the monarch is said to have believed Harry "crossed a line".
The Duke and Duchess of Sussex evicted from Frogmore Cottage last year, and it may have all come down to a two-word insult directed at Queen Camilla.
The king's decision to make Harry homeless in his own country reportedly left him and his wife Meghan Markle "stunned".
There were more than 50 mentions of Camilla in Harry's memoir - and the Duke does not hold back his dislike for 'the Other Woman'.
But his particularly cruel comments were regarding her becoming his "wicked stepmother". Towards the start of the book, Harry explains what life was like after his mother, Princess Diana, died and how his father, King Charles, began to move on.
Prince William's younger brother says he sensed the presence of 'the Other Woman', and that his brother, Prince William, long harboured suspicions about her which confused and tormented him. After using the phrase four times in half a page, Harry finally reveals that 'the Other Woman' is in fact Queen Consort Camilla.
In a TV interview, Harry added: "She was the villain. She was the third person in their marriage. She needed to rehabilitate her image."
Royal sources have claimed Charles took decisive action immediately after being passed a dossier of findings by aides revealing details from the explosive book.
An insider said: "It was the last straw. Harry was well aware how Camilla would be a red line for his father and he crossed with flagrant disregard anyway. The King felt without a doubt it crossed a line – it was the ultimate act of disrespect."
Royal expert and historian Dr Tessa Dunlop told the Mirror: "Britain's response to the news has, on the whole, been gleeful. On one level the vitriol is understandable.
"Prince Harry had just lobbed several verbal hand grenades at his family and the former institution to which he belonged. But he did so from a position of weakness, on the outside, in pain and feeling side-lined."
The expert went on: "A broad-shouldered confident monarchy would have weathered the storm. Instead, by evicting the couple from the Queen's generous gift of Frogmore Cottage King Charles is going directly against the conciliatory style of Her late Majesty."
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