King Charles is fiercely protective of his “beloved” daughter-in-law as she battles cancer alongside him.

Christopher Andersen, author of “The King,” claimed to Fox News Digital that the British monarch has been devoted to providing support for the Princess of Wales behind palace doors.

Middleton, who announced she was diagnosed with an undisclosed form of cancer, has been keeping a low profile as she undergoes chemotherapy. A spokesperson for Kensington Palace previously confirmed to Fox News Digital that the mother of three will return to official duties when “she is cleared to do so by her medical team.”

“There are those inside and outside the palace who have criticized Kate over the years [before her diagnosis] for supposedly not shouldering her share of the royal burden, for not going to as many ribbon cuttings, hospital openings and plaque unveilings as the late Queen Elizabeth II, the king or Princess Anne, for instance,” Andersen explained.

“It has always been Kate’s choice to prioritize her children’s well-being over royal duties,” he shared. “In the past, Charles has remained silent about this and allowed the sniping from the sidelines to continue. But no more. Now the king brooks no criticism of Kate, period.”

Prince William in a navy blazer and matching pants with a white shirt walking alongside his wife and their three children
The Prince and Princess of Wales are parents to three children: Prince George, Princess Charlotte and Prince Louis. (Jonathan Brady – Pool/Getty Images)

“Other royal family members and courtiers alike know that they risk being read the Riot Act by the king if they dare utter a negative syllable about Kate,” Andersen alleged. “Charles has also made it clear that everyone should stand down in terms of when and how she returns to a full public schedule.”

In February, Buckingham Palace announced Charles had been diagnosed with a form of cancer and was undergoing treatment. A “separate issue of concern” was identified during the monarch’s “benign prostate enlargement” procedure at the London Clinic.

“Subsequent diagnostic tests have identified a form of cancer,” the palace said in a statement at the time.

In a video shared in March, the Princess of Wales, 42, revealed that she, too, is battling a form of cancer. Her announcement followed weeks of speculation about her health and whereabouts.

Kate Middleton in a white top with navy stripes sits on a bench to announce she has cancer

Kate Middleton announced to the world she had cancer in a pre-recorded message shared in March. (The Prince and Princess of Wales Twitter)

Middleton asked for “time, space and privacy” while being treated for an unspecified type of cancer that was discovered after what she described as “major” surgery.

Charles said he is “so proud of Catherine for her courage in speaking as she did,” according to a statement released by Buckingham Palace. The king, who received prostate treatment in the same hospital and at the same time Kate had her surgery, remained in the “closest contact with his beloved daughter-in-law.”

The king and Queen Camilla “will continue to offer their love and support to the whole family through this difficult time,” the palace said.

Andersen alleged that Charles was privately impacted by Middleton’s illness.

“Charles was moved to tears by Kate’s stunning video announcement that she has cancer,” Andersen alleged. “The king sees her as, in a word, brave. He also knows better than anyone that the future of the monarchy is to a considerable extent in her hands. She is not only the wife of a future king but the mother of a future monarch. Kate has also shown herself to be unswervingly loyal to the royal family and above reproach – things he can’t always say about other Windsors.”

“The king showed his appreciation several weeks ago by bestowing on Kate the highest accolade he could, making her the first royal ever appointed to the Order of the Companions of Honour,” Andersen said. “Nobody understands more fully than King Charles just how difficult fighting cancer can be – the toll it takes emotionally and physically. The king has made it clear that whatever Kate feels she needs, she gets.”

Author Christopher Andersen says King Charles is ensuring that no one “utters” a negative word about his daughter-in-law. (Richard Pohle/Pool/AFP via Getty Images)

In her speech, Middleton assured the public that she looks forward to returning to royal duties – when she is ready.

“My work has always brought me a deep sense of joy, and I look forward to being back when I am able. But for now, I must focus on making a full recovery,” the princess said at the time.

Charles has since returned to public-facing duties. He and Camilla will be hosting the emperor and empress of Japan for a state visit in June.

King Charles and Queen Camilla wearing red royal robes
King Charles III and Queen Camilla walk down the steps of St. Paul’s Cathedral in London on May 15, 2024. (Chris Jackson/Getty Images)

“He may be chomping at the bit to resume his duties, but the king understands that Kate may take a little more time or a lot,” Andersen added.

Kinsey Schofield, host of the “To Di For Daily” podcast, alleged to Fox News Digital that the king is protective of both of “his girls” – the Princess of Wales and his wife.

“Catherine, the Princess of Wales, is what he considers the daughter he never had,” said Schofield. “Catherine has been such an important part of the family for decades now. She is hard-working, focused, loving, and respected for her contributions all over the world.”

“One blatant example of the king going to great lengths to protect the Princess of Wales is the timing of the announcement of his surgery for an enlarged prostate,” Schofield explained. “The palace wanted to take the heat off the Princess of Wales who had just announced a planned abdominal surgery. After Catherine revealed her cancer scare… the king was the first to publicly support her.… When King Charles gave Catherine, Princess of Wales, the title ‘Royal Companion of The Order of the Companions of Honour,’ that marked a first in British royal family history.”

Charles is known to be very fond of Middleton. During his state visit to Kenya in 2023, the monarch recalled how Prince William proposed to Middleton in the country in 2010. He called her “my beloved daughter-in-law” at his address.

Middleton is also known for showing affection towards the king. During public engagements, the pair exchange hugs and kisses on the cheek.

The king “has always had a very good bond with her,” author Sally Bedell Smith previously told People magazine.

“She’s interested in artistic things, and she appreciates art and culture, so [she] has an affinity with the king over that.”

Smith, who penned “George VI and Elizabeth: The Marriage That Saved the Monarchy,” said the king and princess now have another shared bond over their cancer diagnosis.

“Obviously, they have this in common and can only bring them closer,” she noted. “It is a source of reassurance and consolation for both of them.”

In her announcement, Middleton assured the public that “I am well and getting stronger every day by focusing on the things that will help me heal in my mind, body and spirit.”

“Having William by my side is a great source of comfort and reassurance, too, as is the love, support and kindness that has been shown by so many of you,” Middleton added.