Princess Kate and Prince William are feeling "intense anxiety" amid King Charles's cancer battle, according to a royal commentator.
The King is receiving treatment for a form of cancer and is currently not undertaking public-facing duties.
The Prince and Princess of Wales have also stepped back from royal duties.
Princess Kate announced in March that she had received preventative chemotherapy after cancer was detected in tests following abdominal surgery at the London Clinic.
The Prince and Princess of Wales have also stepped back from royal duties.
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Queen Camilla, Princess Anne, Prince Edward and the Duchess of Edinburgh have stepped up to undertake royal duties in the absence of the King.
Prince William is the heir to the throne and first in the Royal Family's line of succession.
Royal commentator Tina Brown has claimed that William's proximity to the throne is causing the Prince and Princess of Wales "intense anxiety".
Brown wrote in the New York Times: "News of Charles’s cancer has put William and Catherine in frightening proximity to ascending the throne...The prospect of it, I am told, is causing them intense anxiety."
Prince William is the heir to the throne and first in the Royal Family's line of succession.
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However, Brown's claim comes as King Charles is said to be planning to embark on a tour of Australia with Queen Camilla later this year.
The monarch is thought to be considering a two-week state visit to Australia after his cancer treatment started positively.
King Charles is "supercharging" plans for the two-week trip where he would also visit New Zealand and Samoa, according to a royal source.
The insider added the King is "over the moon" that his cancer treatment has started well.
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King Charles is "supercharging" plans for the two-week trip where he would also visit New Zealand and Samoa, according to a royal source.
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A source told The Sun: "The King is raring to go after a significant amount of time off due to his cancer diagnosis.
"He knows he can't hang around and is feeling extremely positive after tests meant he could attend the Easter Sunday service and spend time meeting the public, which he has missed.
"He's over the moon with the way treatment has gone and supercharging plans for Australia, New Zealand and Samoa."