Their tight-knit bond was once so apparent that Prince Harry even once described his sister-in-law the Princess of Wales "the sister I never had".
But now things could not be more different between the pair due to a widening rift between Harry and his brother Prince William - on top of Kate's rocky bond with Meghan Markle. And in his controversial memoir, Harry didn't spare Kate any criticism and revealed private details about a falling out between her and Meghan. He also described how Kate 'grimaced' when Meghan borrowed her lipgloss and how the women had a disagreement after the Duchess of Sussex said William's wife had "baby brain" after Prince Louis was born.
In addition, a racism row has reignited in the wake of Omid Scobie’s tell-all book, Endgame. Dutch copies of the book were pulled from the shelves in the Netherlands when they were found to have identified two individuals said to have questioned the skin colour of Harry and Meghan's son, Archie.
At the time Harry's book hit shelves at the beginning of the year, he sat down for a hard-hitting interview with ITV's Tom Bradby, where he was quizzed about the relationship he had with his brother and sister-in-law. And according to body language expert Judi James, Harry's gestures when talking about Kate appeared to hint at his true feelings towards her.
In the interview, Mr Bradby said the impression was that William and Kate did not get on "almost from the get-go" with his wife Meghan, to which Harry replied: "Yeah, fair." Speaking about his wife, Harry suggested there was a lot of "stereotyping" that even he was "guilty of" at the beginning of his relationship.
And picking up on his body language as he spoke, Judi explained: "There was an air of tragedy about Harry's body language during this long and deeply revealing interview. He ended with verbal assurances that he was 'the happiest I have been', and that he had 'made peace with a lot of what’s happened'. In true US style, he claimed to be in a 'good head space' and that any discussions with his family now wouldn’t leave any 'lingering' thoughts.
"But the man we watched up to this point used conflicting body language signals that made many of his emotions still look rather raw. His gestures and his sound bites and the way he swerved away from some more difficult topics or used non-specific claims suggested anger, resentment and righteousness. But there were also moments when he leaked out more spontaneous signals of love and even humour and fun.
"There was a rather robotic recitation of 'I love my father, I love my brother, I love my family' but when he spoke of his father he appeared close to tears. His account of growing up with his brother regurgitated signals of fun and loyalty and when Kate’s name was mentioned his features softened and his eyes wrinkled into an affectionate-looking eye-smile."
Meanwhile, Harry is in his "worst nightmare" as he and Markle are "back at square one" following the release of Mr Scobie's explosive new book, an expert has claimed.
In recent weeks, it was revealed that Harry's frosty relationship with his father King Charles had shown signs of thawing after the pair enjoyed a 'warm' phone call on the monarch's 75th birthday. At the same time, reports claimed the Sussexes would be keen to receive an invitation to spend Christmas with the royals at Sandringham this year. However, last week new book Endgame was released with a string of new bombshell claims about the royals - including the tension between Harry and Meghan and their royal relatives.
According to royal expert and author Duncan Larcombe, the book couldn't have come at a worse time for Harry and Meghan. He told OK! magazine : "It has put them right back to square one.
"There's now pressure being put on Harry to come out and distance himself from the book, and I think that will be very tempting for him to do because it seems he has been trying to soften his tone towards the royals. There were some green shoots that he might be trying to end the feud from his side. So the timing of the book couldn’t be worse for Harry. I think it's his worst nightmare."
