LONDON — Catherine, Princess of Wales, announced in a personal video message Friday that she has been diagnosed with cancer and that she was in the early stages of chemotherapy.

The news came as a “huge shock,” Catherine said in a prerecorded message posted on X and broadcast on the BBC. “William and I have been doing everything we can to process and manage this privately for the sake of our young family,” she said.

She said that after she underwent major abdominal surgery in January, she thought that her condition was noncancerous.

“The surgery was successful, however, tests after the operation found that cancer had been present,” she said. “As you can imagine, this has taken time. It has taken me time to recover from major surgery in order to start my treatment. But most importantly it has taken us time to explain everything to George, Charlotte and Louis,” she said, referring to her three children, “in a way that is appropriate for them and to reassure them that I will be okay.”

She said that she was undergoing preventive chemotherapy and was focused on making a full recovery. “I am well and getting stronger every day,” she said.

The disclosure comes during a difficult time for royal health. In February, Buckingham Palace announced that King Charles III had cancer. The month before, Sarah Ferguson, the ex-wife of Prince Andrew, said that she had been diagnosed with malignant melanoma, a form of skin cancer.

The palace has not revealed what type of cancer either Charles or Catherine has. In the U.K., 1 in 2 people will develop some form of cancer during their lifetime, according to the National Health Service. The four most common types are breast cancer, lung cancer, prostate cancer and bowel cancer.

Referring to his daughter-in-law, Charles said he was “so proud of Catherine for her courage in speaking as she did.”

Prince Harry and Meghan, The Duke and Duchess of Sussex, said in a statement: “We wish health and healing for Kate and the family, and hope they are able to do so privately and in peace.”

The announcement was her first public address following months of speculation about her health, as she had not made an official public appearance since Christmas. Kensington Palace said in January that she had “successful” abdominal surgery and would not resume her official duties until after Easter. The palace did not disclose what kind of procedure it was, only that it was “planned” and the issue was “noncancerous.”

British Prime Minister Rishi Sunak said in a statement that his thoughts were with Catherine and her family. “The Princess of Wales has the love and support of the whole country as she continues her recovery,” he said, adding that her video address showed “tremendous bravery.”

Sunak said that Catherine had been “subjected to intense scrutiny and has been unfairly treated by certain sections of the media around the world and on social media” since her operation.

Catherine’s time out of the public eye had fueled concern, conspiracy theories and memes about her well-being and whereabouts. In an apparent attempt to quell the frenzy, the palace released a photo showing Catherine, 42, and her three children on Mother’s Day in Britain. But news agencies pulled the photo, citing concerns that it was altered. In a note posted to social media attributed to Catherine, she apologized for editing the photo.

The palace said that Catherine had started her treatment in late February. The cancer announcement on Friday evening would have come after George, 10, Charlotte, 8, and Louis, 5, had finished school for the Easter break.

In her video message, filmed by the BBC, Catherine was sitting on a bench in the gardens of Windsor Castle. In the garden behind her was a bed of yellow daffodils. The flower is often used as a symbol of the fight against cancer.

She was wearing jeans and a sweater, and her voice at times was emotional. “At this time, I am also thinking of all those whose lives have been affected by cancer,” she said. “For everyone facing this disease, in whatever form, please do not lose faith or hope. You are not alone.”

Pietsch reported from Washington.