Photo: ADRIAN DENNIS
By Sean Coughlan of the BBC
King Charles has been diagnosed with a form of cancer, says Buckingham Palace.
It is not prostate cancer, but was discovered during his recent treatment for an enlarged prostate.
The type of cancer has not been revealed, but according to a palace statement the King began "regular treatments" on Monday (GMT).
Buckingham Palace says the King "remains wholly positive about his treatment and looks forward to returning to full public duty as soon as possible".
He will postpone his public engagements and it is expected other senior royals will help to stand in for him during his treatment.
No further details are being shared on the stage of cancer or a prognosis.
Prime Minister Christopher Luxon, who has been at Waitangi Day celebrations, took to X to wish King Charles "a speedy recovery" on behalf of New Zealanders.
Speaking from Waitangi Day commemorations, Labour leader Chris Hipkins said the thoughts of New Zealanders would be with King Charles.
"We all wish him the very best for the road ahead. Many, many New Zealanders will know someone whose life has been affected by cancer and I'm sure we all wish him well."
The King, 75, returned to London from Sandringham in Norfolk on Monday morning (local time) and the palace says he has commenced treatment as an outpatient.
Although he will pause his public events, the King will continue with his constitutional role as head of state.
He is expected to continue to meet UK Prime Minister Rishi Sunak weekly and will also continue to receive and review official red boxes of government paperwork.
There is a constitutional mechanism for when the head of state is unable to carry out official duties - in that circumstance "counsellors of state" can be appointed to stand in for the monarch.
At present that includes Queen Camilla, Prince William, Princess Anne and Prince Edward, with Prince Harry and Prince Andrew no longer to be called on as non-working royals.
Prince William had also temporarily withdrawn from public engagements while he helped his wife Catherine, the Princess of Wales, as she recovered from "abdominal surgery".
But it was announced earlier on Monday (local time) he would return to public duties later this week.
Prince Harry to travel to UK alone
The Duke of Sussex, Prince Harry, has spoken with the King and will travel to the UK to see him in the coming days, BBC News has been told.
The King contacted Prince Harry to tell him of his diagnosis personally.
Prince Harry's last appearance at a royal occasion took place in May, during the King's Coronation.
While Prince Harry and King Charles have had their differences, they have continued to have a relationship with the duke calling his father on his 75th birthday last year.
He will be travelling alone, with his wife Meghan remaining in the US with their two children.
The King was seen at a church service in Sandringham on Sunday, where he waved to crowds.
He had a prostate procedure at a private London hospital more than a week ago.
The King had chosen to go public about his prostate treatment, with the aim of encouraging more men to get prostate checks, the palace said at the time.
He was said to have been delighted to have raised awareness about the issue, with the NHS website reporting a surge in issues about prostate conditions.
For many types of cancer, the chance of getting it increases with age. UK figures suggest, on average each year, more than a third (36 percent) of new cancer cases were in people aged 75 and over.
UK Prime Minister Rishi Sunak wished the King a "full and speedy recovery", alongside Labour leader Sir Keir Starmer.
Australian Prime Minister Anthony Albanese added his well wishes on X, while US President Joe Biden said on the platform that navigating a cancer diagnosis "takes hope and absolute courage".
"Jill and I join the people of the United Kingdom in praying that His Majesty experiences a swift and full reocvery," Biden said.
BBC/RNZ.