Kate Middleton Established Her Own Rules When She Joined the Monarchy to Ensure Family Can 'Always' Be Her 'Priority'

Though Kate Middleton was an outsider when she married Prince William in 2011 and joined the monarchy, author Robert Jobson revealed she wasn't afraid to set boundaries with the royal family.

In his new book Catherine, the Princess of Wales , he spilled that the mother-of-three "even established some fundamental life rules that she would stick to when she joined the Firm."

According to the writer, Kate set out her list of rules in 2015 while pregnant with Princess Charlotte , now 9, but instead of sending a document to King Charles and Queen Elizabeth II , William shared her thoughts with his family on her behalf.

Kate, 42, "wanted space to grow into her role and said she needed more time to adapt to the peculiarities of royal life," Jobson wrote of one of her requests.

"She was clear from the outset that she would not be pigeonholed into carrying out particular duties and insisted on having her full quota of maternity leave, away from the glare of the media and public ," he explained.

Added Jobson, "Her priority, she emphasized, would always be her family."

That's held true even after she started "preventative treatment" for cancer, something she first discussed in March.

Though the royal has returned to the spotlight since her diagnosis, she is still putting most of her royal duties on the back-burner.

"My understanding is that people are going to have to get used to seeing a lot less of Kate. The priority for her now is going to be family and the children," an insider told a news outlet. "The youngest of those kids, Louis , is only 6."

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"Like a lot of people who have a brush with mortality , Kate is going to prioritize the things that matter to her from now on," the source said. "In her case, that means her kids."

The mother-of-three is doing her best to maintain a sense of normalcy for the family, which is one of the reasons she and Charlotte went to a Wimbledon match last month, where the Princess of Wales receiving a standing ovation.

"Now, more than ever, sports provide a much-needed distraction from the pressures of royal life — and from the harsh reality of the health challenges being faced by Kate and King Charles III," author Christopher Andersen said in a previous interview, also referencing the patriarch's cancer battle that was revealed in February.

Fox News obtained excerpts from Jobson's book.