“She feels their feud has gone on long enough and that it’s time for William and Harry to be brothers again. She believes there’s still time to repair the damage and has been quietly pushing for a truce," a source shared.
According to the insider, Kate, 41, was inspired by Princess Diana's diaries, which gave her insight into Harry and William's relationship.
“Diana was a very expressive writer, and her diaries became a source of comfort as her marriage to King Charles III fell apart,” explained the source. “Kate has read them, and they’ve provided valuable insight into what William and Harry’s relationship was like when they were young, and how close they got after their beloved mom died.”
“Kate is telling William to stop being so stubborn,” said a source. “The way she sees it, family is family.”
The brothers have been on bad terms ever since Harry, 38, aired out his family's dirty laundry in his tell-all, Spare, and in his docuseries, Harry & Meghan.
"Two years older than me, Willy was the Heir, whereas I was the Spare," Harry wrote in the tome.
As OK! previously reported, Kate has been trying to bring the boys together for a while.
"I'm not sure how much dialogue there is with William and Harry at the moment, I think the only person that is helping the situation is Catherine, who is doing a brilliant job," expert Robert Jobson said in an interview.
"First of all, when the king wants to see his grandchildren, for example, it's important to say that a lot of it has been through Catherine," he continued.
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"I think as brothers they are more likely to get on the phone and have a conversation. It's quite possible that one of them might pick up the phone to have a rant, but who's gonna pick up the phone on the other end?" he continued. "Because that's not gonna achieve anything."
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Star spoke to the insider.