Prince Harry and Princess Kate were once very close, with the Duke of Sussex even saying she was “the sister I never had” – but one comment reportedly broke the Duchess of Cambridge’s trust.

Prince Harry appears to be in a spat with nearly the whole Royal Family, including his father King Charles, brother Prince William, and even his once chummy sister-in-law Princess Kate could also see their bond beyond repair.

The Duke of Sussex, who used to consider the Princess of Wales as “the sister I never had”, seems to have seen their close ties unravel following the revelations in his explosive memoir Spare, where he kept no secrets.

Post book release, the atmosphere among the royals has reportedly become markedly strained. It was, seemingly, a particular “snide remark” by Harry that shattered Princess Kate’s trust, intensifying the Royal divide.

One expert on Royal affairs suggests that Harry’s comment means Kate is unlikely to be quick to mend bridges with her brother-in-law.

Royal commentator Katie Nicholl reflected on the tension between Prince Harry and Princess Kate to the Sun, noting they were once “very very close” until Harry and Meghan’s departure from senior Royal duties.

Nicholl remarked: “When you think of the personal revelations, and I think you can call them snide remarks made about Kate in Spare, Harry broke the one rule and that is staying silent on family matters.”

Speaking further to the Sun, Nicholl observed: “While Kate and Harry used to be very, very close, there’s been a complete breakdown of that relationship.”

“I don’t think Kate does angry. I think it is more a case of feeling very disappointed, very let down and feeling hurt knowing that she had no right of reply – and Harry knew full well she had no right of reply.”

In contrast to his wife, Ms Nicholl stated that Prince William was “very angry” at his brother for involving Kate in the situation, believing that she was “blameless throughout”.

Ms Nicholl further commented: “[Kate] acted very much as the peacekeeper, she tried to get the brothers back on an even keel and for Kate to be dragged into this mucky saga was upsetting for her and certainly did infuriate William.”

While discussing Meghan Markle, the expert also noted: “I think it’s too far down the line for Kate and Meghan. There were some deeply personal revelations about Kate in the book.”