Kate Middleton’s Cancer Diagnosis Was a 'Heck of a Shock' to Her 'Tight' Inner Circle

Kate Middleton surprised the world when she announced she was diagnosed with cancer, but her friends were equally surprised by the news.

"It was a heck of a shock," an insider told an outlet. "The circle of knowledge was very tight. "

On Friday, March 22, Kate returned to Instagram to update fans on her well-being.

"I wanted to take this opportunity to say thank you personally for all the wonderful messages of support and understanding whilst I've been recovering from surgery," Kate began. "It has been an incredibly tough couple of months for our entire family. In January, I underwent major abdominal surgery in London. 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 I should undergo preventive chemotherapy, and I am now in the early stages of that treatment."

The Princess of Wales continued: "This of course comes as a huge shock, and William and I have been doing everything we can to process and manage this for our young family. It has taken my time for me to recover from my surgery. Most importantly, it has taken us time to explain to George, Charlotte and Louis and to reassure them I am going to be OK. As I've said to them, I am well. Having William by my side is a great source of comfort, and the love and support and kindness that has been shown from so many of you. As a family, we need some time, space and privacy while I complete my treatment. My work has always brought me a deep sense of joy. I must focus on making a full recovery. At this time, I am also thinking of those whose lives have been affected by cancer. Please do not lose faith or hope. You are not alone."

OK! previously reported a rep for Kate and William shared the couple was moved by the public's response to the mom-of-three's condition.

“The Prince and Princess are both enormously touched by the kind messages from people here in the U.K., across the Commonwealth and around the world in response to Her Royal ­Highness’ message,” a spokesperson shared.

As Kate focuses on her health, an insider revealed William is worried about his wife.

“William is trying to be there for Kate and helping in every way he can,” a source told an outlet. “He’s been doing schoolwork with the kids and spending time with them in the afternoons and evenings.”

“They know their mother is sick and is trying to get better,” they added, referring to William and Kate's three kids.

The source added that the future king feels "helpless and scared."

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Insiders spoke to People.