Prince William and Prince Harry have been directly told about King Charles III's cancer diagnosis.
All members of the Royal Family were personally informed about the 75-year-old monarch's health update.
A statement from Buckingham Palace was released at 6pm confirming his diagnosis following separate treatment for a "benign" prostate enlargement.
The Duke of Sussex will fly back to London in the coming days.
Prince William and Prince Harry with an inset of King Charles
GETTY/BUCKINGHAM PALACE
The Prince of Wales has also been in regular contact with his father, a spokesperson has said.
A source close to the Duke of Sussex also confirmed he has spoken with the King about his diagnosis.
Prince Harry and his wife Meghan Markle relocated to the US in 2020 following the fallout of a feud in the Firm.
The Duke and Duchess of Sussex quit royal duties and subsequently settled in California after a stint in Canada.
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Buckingham Palace released a full statement on King Charles' cancer diagnosis
BUCKINGHAM PALACE
King Charles left hospital last week after an operation on an enlarged prostate.
Buckingham Palace noted it was during this procedure that a "separate issue of concern was noted".
In a statement, Buckingham Palace issued a health update confirming Charles' cancer diagnosis.
It said: "During The King’s recent hospital procedure for benign prostate enlargement, a separate issue of concern was noted.
Prince William and Prince Harry have been told about King Charles' diagnosis
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"Subsequent diagnostic tests have identified a form of cancer.
"His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties.
"Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual.
"The King is grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure.
King Charles was last seen in public during a walk in Sandringham yesterdayGETTY"He remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible.
"His Majesty has chosen to share his diagnosis to prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer."
King Charles' previous announcement ahead of his separate treatment sparked 26,170 visits to the enlarged prostate page on the NHS website.
The figure was up to a daily average of 1,400 earlier in the week.
King Charles wore a sombre expression as he waved to crowds while walking alongside his wife Queen Camilla at St Mary Magdalene Church in Sandringham yesterday.
Prince William will step in for some of King Charles' duties
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Prince William could be "taking on some of King Charles's duties" after it was announced that the monarch has been diagnosed with cancer.
GB News royal correspondent Cameron Walker said: "Prince William, I'm told, is also possibly going to be taking on some of King Charles' duties or representing the King of behalf of him, but certainly not all.
"The king is still expected to have his weekly audience with the Prime Minister, but on doctor's advice, it's advised that they should not meet in person.
"Other arrangements, it's understood, will be arranged and similar with privy council meetings, the king is still expected to attend privy council meetings.
"He's also expected to work through those famous red boxes, his constitutional duties, signing Government papers, reading cabinet minutes."