Kate, Britain's Princess of Wales, said on Friday she was undergoing preventative chemotherapy after tests taken after she had major abdominal surgery in January revealed that cancer had been present.
Kate, the 42-year-old wife of heir to the throne Prince William, called the cancer discovery a "huge shock". The news comes as a fresh health blow to the British royal family: King Charles is also undergoing treatment for cancer, reports BBC.
Kate spent two weeks in hospital in January after undergoing what her office said at the time was successful, planned surgery for an unspecified but non-cancerous condition.
However Kate said in a video message that subsequent tests had revealed cancer had been found. She said she was well and getting stronger.
"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," said Kate.
She was dressed in jeans and a jumper and looked pale and tired in the video, which was filmed on Wednesday.
"This of course came as a huge shock, and William and I have been doing everything we can to process and manage this privately for the sake of our young family."
Following her operation, the palace had said the princess would not return to official duties until after Easter, which falls at the end of this month. But her absence from public life has provoked intense speculation and wild rumours on social media.
King Charles, 75, underwent a corrective procedure for an enlarged prostate at the same hospital as Kate in January. Buckingham Palace then revealed in February that he was to have treatment for cancer, meaning he has had to postpone his public royal duties.
"His majesty is ‘so proud of Catherine for her courage in speaking as she did'," a Buckingham Palace spokesperson said, saying Charles had been in close contact with Kate since they were at the private London Clinic together in January.
"Both their majesties ‘will continue to offer their love and support to the whole family through this difficult time’."
Prince Harry, who has fallen out with William since he moved to California with his wife Meghan, sent a message of support.
"We wish health and healing for Kate and the family, and hope they are able to do so privately and in peace," Harry and Meghan, the Duke and Duchess of Sussex, said.
Similar statements also poured in from British political leaders, and from the office of U.S. President Joe Biden, for the princess, who is popularly known by her maiden name Kate Middleton.
Kate's office, Kensington Palace, said it would give no further details about the type of cancer that had been found, saying the princess had a right to medical privacy. It said she was on a recovery pathway and the preventative chemotherapy had begun in February.