Royal siblings Prince Charles and Princess Anne haven’t always seen eye to eye.
WATCH: Prince Charles sneaks up on Princess Anne during royal function
When it came to his sister’s first marriage to Mark Phillips in 1973, Charles thought Anne was making a “dreadful mistake”.
Author Howard Hodgson revealed how the Prince of Wales truly felt about his younger sister’s decision to marry in his 2007 biography, Charles: The man who will be King.
Mr Hodgson wrote: “[Charles] was still reeling from [Camilla’s] engagement when in May he received a letter from his father informing him that his sister Princess Anne, was to marry an army captain called Mark Phillips.”
Charles was in Antigua to train with the Royal Navy when he heard the news, which came as a double blow after he found out that his love Camilla Chand, who he was dating before he left, was to marry Andrew Parker Bowles.
The author explained: “Not only was Charles convinced that Anne was making a dreadful mistake, but it appeared to him that while the Royal Navy held him captive in the Caribbean, everything that was dear to him at home was being taken away from him and there wasn’t a thing that he could do about it.
“Although he didn’t enjoy a close relationship with either of his parents, he had come to see his family as something very dear and something to which he had been denied close access for long periods of time since the age of seven.”
Mr Hodgson pointed out how Anne had become “a close confidante” for Charles as well as a person “with whom he could play the fool”.
News of her marriage meant that he would no longer “have first call on her affection”.
Mr Hodgson continued: “Initially he found this very hard to accept and it took him several days to be able to contemplate her marriage without a sense of despair.”
Anne married Mark on November 1, 1973. They couple went on to have two children, Peter and Zara.
Their marriage didn’t last, however, and they split in 1989, finally divorcing in 1992.
It’s not the first time the siblings have fallen out.
According to Anthony Holden’s 1979 biography of Charles’ early life there was an incident when Anne came up close and personal with a group of anti-blood sport protestors as she was preparing to go fox hunting.
Writing in Charles, Prince of Wales, Anthony claimed one angry taxpayer confronted her and, addressing the Princess Royal, asked: “Who’s paying you to do this?”
On hearing about the incident afterwards, Charles is said to have “groaned” at this point in the story because he “knew what was coming next”.
The author claimed the row came to an end when Anne decided enough was enough and looked to move on but, as she did so, a protestor shouted: “Well we’re paying you to do that!”
Charles is said to have been extremely disparaging of his sister’s behaviour as he considers confrontations with the public to be a “royal sin”.
Mr Holden adds that Charles was often disgruntled at news of Anne’s public outbursts against photographers, which he considered “counter-productive”.