Kate Middleton has made a point to put her family first.
While the Princess of Wales was expanding her family with Prince William, she established a few strict rules with Queen Elizabeth II, according to royal author and journalist Robert Jobson.
"Catherine knows her own mind and even established some fundamental life rules that she would stick to when she joined the Firm," Jobson wrote in his new book, "Catherine, the Princess of Wales," obtained by Fox News Digital.
As Jobson explained, her "terms" were presented to Queen Elizabeth II and then-Prince Charles in 2015 while she was pregnant with Charlotte, her second child.
Although the "life rules" weren’t in "some formal document but by Prince William," Middleton made important agreements with the royal family.
On her behalf, Prince William explained that Middleton "wanted space to grow into her role and said she needed more time to adapt to the peculiarities of royal life," according to Jobson.
"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. Her priority, she emphasized, would always be her family."
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The mother of three has strongly demonstrated that she is loyal to the royal family and a loving mother to Prince George, Princess Charlotte and Prince Louis.
While the Princess of Wales has always remained dedicated to her royal duties, she has kept a low profile since she publicly announced her cancer diagnosis in March.
As Middleton prioritizes her children this summer amid her cancer battle, she doesn't want the royal family to "worry."
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She made a triumphant return to public duty this summer during her first appearances since her diagnosis — Middleton attended the Trooping the Colour in June and went to Wimbledon in July.
In June, Christopher Andersen, author of "The King," told Fox News Digital that the summers have always been vital for the 42-year-old and her husband, Prince William, heir to the British throne. Their goal has always been to give their children as much normalcy as possible, away from the peering eyes of the press.
"Kate and William have always made the most of their summers with the children," said Andersen.
"The side effects of chemo are bound to make that level of participation more daunting for Kate, but she’s not about to let that spoil the children’s summer," said Andersen. "… Kate doesn’t want them to worry about her — she’s always believed it’s her job to worry about them — and that means keeping George, Charlotte and Louis busy with the sort of things — horseback riding, swimming, having sleepovers with cousins and schoolmates — that they always do during their vacation break."
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The Princess of Wales announced she was undergoing treatment for cancer in March after undergoing planned abdominal surgery in January.
"The princess is not expected to return to work until it's cleared by her medical team. Early childhood will continue to be central to her public work," a Kensington Palace spokesperson previously told Fox News Digital.
In January, Buckingham Palace announced King Charles would undergo outpatient treatment for a benign enlarged prostate and then, in February, the palace revealed he also had cancer.
Charles initially stepped away from his royal duties during his cancer treatment, but returned at the end of April with a reduced schedule.
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Fox News Digital's Stephanie Nolasco contributed to this report.
