Catherine, Princess of Wales, on Friday announced that she has cancer and is in the early stages of chemotherapy, asking for "time, space and privacy" as she completes her treatment.

Kate, as she is widely known, said the discovery of cancer, after successful abdominal surgery in January, was "a huge shock" but she was "well and getting stronger every day".

The disclosure came after royal officials said in early February that King Charles III was being treated for cancer, forcing him to cancel all public engagements.

Charles said he was "so proud of Catherine for her courage in speaking as she did", leading messages of support, including from UK Prime Minister Rishi Sunak and the White House.

Like Charles, the 42-year-old princess, whose husband Prince William is heir to the throne, did not disclose the exact nature of the cancer.

But she described the last few months since she went into hospital as "incredibly tough" for her, William and their three young children.

"In January, I underwent major abdominal surgery in London and at the time, it was thought that my condition was non-cancerous," she added in a video statement, filmed on Wednesday at Windsor, west of London, where they live.

"The surgery was successful. However, tests after the operation found cancer had been present.

"My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment."

Preventative chemotherapy is given "after an operation to prevent recurrence", said Shivan Sivakumar, associate professor in oncology at the University of Birmingham in central England.

"This is to attempt to destroy any circulating cancer cells," he added.

- Absence -

Kate -- one of the most photographed women in the world -- is a central figure in the royal family and married Prince William, 41, in 2011.

She said it had taken them time to explain the situation to Prince George, aged 10, Princess Charlotte, eight, and five-year-old Prince Louis, "and to reassure them that I am going to be OK".

"As I have said to them; I am well and getting stronger every day by focusing on the things that will help me heal; in my mind, body and spirits," she added.

Her Kensington Palace office said she was "focused on making a full recovery" and would return to official duties "when she is cleared to do so by her medical team".

William, Kate and their children are seen as the modern face of the British royal family, and key to its future as it faces declining support among younger people and increasing republican sentiment.

She was last seen at a public engagement on December 25, when she joined the king and other senior royals at a Christmas Day church service.

Kensington Palace announced on January 17 that she was facing up to two weeks in hospital and several months' recuperation following abdominal surgery.

She was not expected to be ready to return to public duties until after Easter on March 31, a statement at the time said.

Royal officials did not disclose the exact nature of her condition but said it was not cancer-related.

- Charles diagnosis -

That announcement came shortly before a separate statement from Buckingham Palace that 75-year-old Charles was to have surgery for a benign enlarged prostate.

He later spent three days at the same private hospital in central London. Officials then said in early February that tests had identified "a form of cancer", without giving further details.

The king has cancelled all public engagements except audiences with the prime minister and ambassadors, and worked on official papers while undergoing treatment.

He has been photographed several times since then, and seen attending church.

But there has been rampant speculation online about Kate's health and whereabouts, particularly online.

She was not seen arriving or leaving the hospital, and William was only spotted visiting once.

Rumours and gossip grew further on March 11, after she released a Mother's Day photograph that was later found to have been digitally altered.

Kate, who has taken several official photographs that have been distributed to the media, apologised in a statement after leading news agencies, including AFP, pulled the image.

A week later, British media published new images of the princess walking with William at a farmers' market near their Windsor home.

This week, there were claims that an attempt may have been made to access Kate's confidential medical records, prompting a referral to the UK's data protection watchdog.