Prince William laid important groundwork for his marriage with Princess Kate to succeed

However, after they tied the knot, Kate laid out some “terms” that would ensure she would only carry out duties that were close to her heart. These conditions would allow her to balance both being a working royal and focusing on her family.

Robert Jobson, a royal commentator, detailed the arrangements in his new biography, Catherine, Princess of Wales.

He explained that Prince William approached his father and Camilla to detail the “fundamental rules” on Kate’s behalf, who was pregnant with Princess Charlotte at the time.

In an excerpt from the book, which is due to be published next month, the royal commentator said: “On her behalf, he explained that she wanted more space to grow into her role and needed more time to adapt to the peculiarities of royal life.”

Going into more details about her wishes, Jobson explained: “Before joining 'the Firm', she wisely established some fundamental rules. She wouldn't be pigeon-holed into carrying out particular duties and insisted on eventually having her full quota of maternity leave, away from the glare of the media and public.

“Her priority, she emphasised, would be to maintain a balance between her royal obligations and what she held most dear: a loving marriage and a happy family life.

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“This didn't mean that she wouldn't carry out royal duties; far from it. But she wanted to offer her patronage only to charities close to her interests and delve into their purpose with in-depth study.”

Robson said that William’s interference on Kate’s behalf was poignant as he knew that his mother, the late Princess Diana, had often felt like an “outsider”, a position he did not want his wife to inherit.

During an interview following their engagement in 2010, the Princess was asked if she found it intimidating to be following in the footsteps of a “massive iconic figure” - replying that she did indeed.

William then stepped into her defence to say: “No one is going to try to fill my mother's shoes — what she did was fantastic. It's about making your own future and your own destiny, and Kate will do a very good job of that.”

Ahead of their 13th anniversary, a royal commentator said the Waleses will not celebrate the same way as usual due to Kate’s health.

Richard Fitzwilliams told GB News in April: “They will undoubtedly be celebrating their 13th wedding anniversary privately.

“This year will be very different from previous years as Catherine is undergoing preventative chemotherapy after recovering from abdominal surgery.”

Fitzwilliams continued: “This is clearly a marriage of like minds as the years have shown. They are focused on parenthood with its ups and downs and ensuring their children grow up in as normal a way as possible.”