Meghan Markle and Prince William allegedly had a row after she made a comment about Kate's hormones when her sister-in-law was pregnant with Prince Louis, Prince Harry claims.
In a leaked extract of his tell-all memoir Spare, which will be published in the UK next week, the Duke of Sussex claims that in the run-up to his wedding in 2018, Meghan told the Princess of Wales that she must have "baby brain".
The remark went down like a lead balloon and in a bid to move past the incident, the couples met up - but this led to a row between William and Meghan, the book claims, where he apparently said she was 'rude'.
In the book, Harry recounts how Kate was upset and therefore Meghan apologised and explained that is how she speaks to her friends, the Sun reported.
But Harry says William "pointed a finger at Meg", then allegedly blasted: "Well, it's rude, Meghan. These things are not done here."
Meanwhile, the Duke of Sussex also accuses Prince William of calling Meghan 'difficult' in his memoir - a trope Meghan says is often used to describe women of colour and has recently discussed in her podcast Archetypes.
Amid the accidental leak of the book in Spain, we've taken a look at the Prince of Wales' relationship with Meghan - from awkward body language to what look to be reconciliation attempts.
Nervous first meeting
With Meghan coming from a completely different world in the US compared to that of William and Harry, along with their privately-educated circle, the former actress was fully expecting a grilling from her boyfriend's brother on their first meeting.
Despite her nervous anticipation, the two got off to a good start and William paid her a compliment, according to insiders.
In Finding Freedom, biographers Scobie and Durand wrote: "Meghan thought that William would no doubt want to know everything about her and her intentions. She was self-aware enough to understand that the brothers were wary of women who were more interested in their titles than their well-being.
"...She had thought the entire meeting through, she told a friend."
They added: "It wasn't that. William first said to her, 'I was looking forward to meeting the girl who has put that silly grin on my brother’s face.'
"Overall, Meghan and William got 'along so well.'"
Raising concern
A royal expert previously claimed Prince William gave a warning to his younger brother about how things were moving with Meghan - which might have been the reason for early signs of tension between the pair.
There have been numerous reports of a rift between the Prince and Princess of Wales and the Duke and Duchess of Sussex - once dubbed the fab four.
Author Katie Nicholl believes things haven't been right between the brothers since William made a comment to Harry about Meghan.
She claims Harry took William's concerns to heart and as a criticism, rather than looking out for him.
Speaking on Channel 5 documentary Princesses At War, she said: "William was quite concerned that the relationship had moved so quickly."
She says William asked Harry: "This seems to be moving quickly, are you sure?"
"Harry is hugely protective of Meghan, he saw that as criticism, he interpreted that as his brother not really being behind this marriage.
"I don't think things have been quite right ever since."
'Jarring' first dinner
In the first part of Meghan and Harry's Netflix series - Harry & Meghan - the former actress recalled her first meeting with the Prince and Princess of Wales and how they got together for dinner.
She said: "When Will and Kate came over, and I met her for the first time, they came over for dinner, I remember I was in ripped jeans and I was barefoot.
"I was a hugger. I've always been a hugger, I didn't realise that that is really jarring for a lot of Brits.
"I guess I started to understand very quickly that the formality on the outside carried through on the inside.
"There is a forward-facing way of being, and then you close the door and go ‘You can relax now’, but that formality carries over on both sides. And that was surprising to me."
Body language expert Darren Stanton watched the clip and said it was clear Meghan felt a sense of embarrassment over the encounter.
Speaking on behalf of Betfair Casino, Darren said: "Meghan is extremely kinaesthetic, which means that she is a very tactile person who likes to touch. However, this is clearly not the case with a lot of people in life.
"...As Meghan was talking about the moment, I noticed her eyebrows came up and her face dropped.
"This was a combination of the emotions of feeling embarrassed and shame. When she was repeating the memory about the meeting, her unconscious mind was fighting off the same feelings that she had back then."
'Distancing himself'
During Christmas celebrations at the Sandringham estate in 2019, Prince William appeared to be 'distancing' himself from his sister-in-law, according to psychologist and body language expert Darren Stanton.
Some royal fans had spotted that William and Meghan looked a little distant from one another in photos, in contrast to previous celebrations where they were seen laughing with each other as they left St Mary Magdalene Church.
Stanton told Express.co.uk at the time: "William's body language is quite interesting because as soon as he registers Meghan is besides him he immediately distances himself over to his far right."
The expert called this "distancing behaviour", adding it is "generally unconscious when someone's in a situation they want to escape from... Personal or physical distance is one of the first things they will do."
He continued: "I also notice there appears to be no dialogue, this is in stark contrast to last year when we observed William interacting with Meghan.
"There is clearly an issue as William was probably upset with Meghan if the rumours are true about Meghan and Kaye having a feud."
Unusual gift
There have been glimmers of a close bond and one of them was with Meghan's unusual Christmas gift for Prince William, which could have been her way of making light of the feud rumours.
The Duchess reportedly gifted her brother-in-law a spoon engraved with the words 'cereal killer' as a joke present to use for his breakfast - and it went down well.
According to Omid Scobie and Carolyn Durand's biography about the couple, Finding Freedom , Meghan struggled with ideas for her the royal family during her first Christmas as part of The Firm.
"Meghan's biggest challenge was finding the perfect novelty gifts to amuse her new extended family," authors Omid Scobie and Carolyn Durand write.
"At least one of her gifts was a huge hit – a spoon for William that had 'cereal killer' embossed on the shallow bowl end of the utensil."
'Encouraging gesture'
More recently, body language experts claim the Prince of Wales wanted to comfort Meghan on her return to the UK following the Queen's death.
The foursome reunited in September to view floral tributes to the Queen and greet well-wishers at Windsor Castle, where they reportedly put their differences aside to carry out the walkabout.
According to body language expert Judi James, William appeared as the leader of the group and offered a touching gesture to Meghan.
She told the Mirror: "There were moments of communication between the four and it was obvious that this was William’s decision and instigation.
"He led the choreography and he was the one to hold out an arm to gesture Meghan to join the group and be introduced to their host."
Judi noted that Harry and Meghan appeared a little apprehensive at first but managed to relax into their roles.
She added: "There were no add-on tie signs between the two couples to suggest anything fonder or more affectionate had been achieved behind the scenes. Eye contact was minimal and chatting reserved to a very few words.
"On a scale of bonding it was just above the level of perma-frost we saw at the Commonwealth day service in 2020 but no higher than the chats between the brothers at both Prince Philip's funeral and the unveiling of Princess Diana’s statue.
"But as public statements go it was phenomenal and probably broke some very important ice in terms of any appearances to come over the next very tragic week."
Kensington Palace and Buckingham Palace have so-far declined to comment on the leaked claims from Harry's book - which emerged five days before is due to be published.
This story is based off a translated version of Prince Harry ’s book Spare - which is set to be published in the UK on January 10 and is available to purchase on Amazon.