James Middleton has a "close" relationship with Kate and Prince William, a royal commentator exclusively told GB News.
The younger brother of the Princess of Wales took to Instagram immediately after Kate, 42, announced she had been battling cancer.
The 36-year-old wrote: "Over the years, we have climbed many mountains together.
"As a family, we will climb this one with you too."
The Princess of Wales had recorded a video from her garden at Adelaide Cottage to release to the public.
In the video, she disclosed her diagnosis saying: "In January, I underwent major abdominal surgery in London and at the time, it was thought that my condition was non-cancerous.
"The surgery was successful. However, tests after the operation found cancer had been present.
"My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment."
Gareth Russell spoke exclusively to GB News about James's relationship with Princess Kate, following his emotional Instagram post.
He said: "I think the Middleton family are generally very admired for their decency and discretion, ever since their daughter's marriage into the Royal Family.
"We know that they do have a close relationship with Prince William and with Catherine's children.
"All the evidence we have suggests a very loving and close relationship with the family."
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The commentator added: "But certainly they're not ones to sit down and talk and tell interviews or anything like that.
"Every evidence we have suggests it is a close relationship.
"The fact you don't see a lot of these sit-down interviews or quest for publicity from the family is probably an indicator of how close they are.
"It certainly explains why they are so highly thought off by many people in Britain."
