A 45-minute catch-up with Harry: The latest in King Charles' cancer diagnosis.

This week, Buckingham Palace announced King Charles had been diagnosed with cancer and would postpone public appearances.

Charles, 75, had spent three nights in hospital last month after undergoing a corrective procedure for an enlarged prostate, when a separate issue of concern was discovered and identified by further tests as cancer.

The palace did not give any details about Charles' cancer but a royal spokesperson said that it was not prostate.

Earlier this week, Prince Harry flew into London from Los Angeles to see his father.

They reportedly met on Tuesday for less than an hour, before Charles and Queen Camilla flew by helicopter to the royal estate in Sandringham.

Harry then stayed at a London hotel overnight and flew back to the United States the next day.

He did not see his brother Prince William, who has this week returned to royal engagements for the first time following wife Kate Middleton's stay in hospital.

The King has started a schedule of regular treatments but has been advised to postpone his public-facing duties.

He will carry on working behind the scenes on state business and official papers.

"The King is grateful to his medical team for their swift intervention, which was made possible thanks to his recent hospital procedure," the Buckingham Palace statement said.

"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."

Charles was discharged from The London Clinic a week ago after undergoing treatment on an enlarged prostate.

Buckingham Palace announced on January 16 that the King was to have treatment for an enlarged prostate but that the condition was benign.

The palace announced the King's cancer diagnosis at 6pm on Monday.

Buckingham Palace said that the King chose to share his cancer diagnosis to "prevent speculation and in the hope it may assist public understanding for all those around the world who are affected by cancer".

According to the NHS, his decision to be transparent about his health has resulted in a boost to public awareness.

On the day after the announcement about his enlarged prostate diagnosis, there were 16,410 visits to the NHS website's prostate enlargement page compared with 1,414 visits the previous day.

Charles, who acceded to the throne just 17 months ago, was last seen on Sunday when he attended church in Sandringham.

with AAP and PA.