The relationship between the two brothers has been confirmed by Harry to have broken down in recent years as the Sussexes stepped back from the Royal Family.
"She brings a reassurance to that relationship," Valentine Low, author of Courtiers, said. "She was often the peacemaker, or tried to be the peacemaker, with Harry. You saw that after Philip's funeral, when she kind of brought the brothers together."
Prince Philip died in April 2021 in the midst of the COVID-19 pandemic, and his socially distanced funeral saw both Harry and William walk in the funeral cortege – separated by their cousin Peter Phillips – before sitting apart during the service.
Once the service was complete, Kate was seen engaging Harry in conversation, who the Sunday Times reported at the time, "seemed to visibly relax, no longer alone".
The pair were joined shortly afterwards by William, which continued for at least the portion of the walk back to Windsor Castle that was caught on camera, with Kate eventually dropping back to leave them to it.
Philip's funeral came weeks after Meghan and Harry's bombshell interview with Oprah Winfrey that laid bare their grievances with the royal "institution" and the media, offering some explanation about their motivations for leaving life as working royals behind.
Low – speaking on the Scandal Mongers Podcast – also touched on new revelations from the new paperback edition of his book Courtiers, which claimed Kate was the member of the family most keen to use the now-infamous phrase "some recollections may vary" in the Royal Family's response to the Sussexes' interview with Oprah.
"A lot of authors have been claimed for that phrase, obviously it wasn't the Queen's own phrase [...] It turns out that was William's private secretary, Jean-Christophe Gray, he came up with it. He only started in the job three weeks earlier, he was incredibly new to it when this whole Oprah Winfrey crisis came along."
Low also said that while the Queen was waiting to respond until she had watched the interview broadcast in full, aides had prepared a draft response, which "challenged the truth of what Harry and Meghan had to say" which included the "recollections may vary" phrase.
"There was a debate about it amongst all the courtiers and the various royal households and some people in other households were a bit nervous, they didn't think they should include it because they were worried that it would unnecessarily antagonise Harry and Meghan.
"But, the person who was adamant that it should stay in was Kate [...] because she made the argument that 'we've got to lay down a marker to say that we challenge some of this narrative because otherwise it's going to be accepted as true and we've got the future reputation of the Royal Family to think about'.
"It shows a side of Kate that's not always appreciated – that she's far steelier... she's thinking about the longer term."
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