Catherine, Princess of Wales, has been diagnosed with cancer and has begun chemotherapy, she announced Friday, putting a grim coda on months of rumors about her condition and plunging Britain’s royal family into deep uncertainty as two of its most senior figures grapple with grave health concerns.

Her diagnosis follows that of King Charles III, who announced his own cancer diagnosis and treatment in early February. Like the king, Catherine, also known as Kate, did not specify what type of cancer she had nor what her prognosis was.

Speaking in a prerecorded video released Friday evening, Kate said, “It has been an incredibly tough couple of months for our entire family,” as she described having major abdominal surgery in January and then learning through subsequent tests that she had a form of cancer.

Looking fatigued but determined to express hope about her recovery, Kate, 42, said she and her husband, Prince William, were helping their three children, George, Charlotte and Louis, cope with having a sick mother.

“This of course came as a huge shock,” Kate said, “and William and I have been doing everything we can to process and manage this privately for the sake of our young family. As you can imagine, this has taken time.

“We hope that you will understand that, as a family, we now need some time, space and privacy while I complete my treatment,” said Kate, who wore a simple striped sweater and sat on a bench, against a backdrop of early spring flowers, in the video, which was recorded by BBC Studios on Wednesday.

Kate’s announcement landed with a thunderclap in a country where popular members of the royal family — and Kate is assuredly one — are still sometimes treated like members of every British family. It drew an outpouring of sympathy from public figures and ordinary people, for many of whom Kate symbolizes the royal family’s future — a glamorous but also relatable figure, born outside the monarchy, who became a princess and mother in the unsparing glare of the public eye.

The announcement also put a stop, at least for now, to the torrent of rumors and conspiracy theories that have coursed through social media and the news media about Kate’s condition and even whereabouts. But as with Charles, Kate’s announcement left many questions unanswered.

Palace officials offered no details on the type of cancer, how far it had progressed or how long she would receive chemotherapy. A spokesperson said she had begun the treatment in late February and was on a “recovery pathway.” Officials asked the news media not to speculate about her condition, in a perhaps futile attempt to forestall a new round of questions.

But any expectation that Kate would return to official duties after Easter, as the palace once said, seemed gone. A palace official said it would not be sharing further private medical information about Kate, adding that the princess had a right to medical privacy, “as we all do.”

For the royal family, Kate’s cancer is another heavy blow, sidelining one of its most visible figures at a time when its ranks were already depleted. In addition to Charles, who has canceled public appearances to undergo his treatment, the family has been adjusting to the loss of Queen Elizabeth II, who died in 2022; the departure of Prince Harry and his wife, Meghan; and the exile of Prince Andrew, disgraced by his association with convicted sex offender Jeffrey Epstein.

Harry and Meghan issued a statement saying they wished “health and healing for Kate and the family, and hope they are able to do so privately and in peace.”

Buckingham Palace said Charles was “so proud of Catherine for her courage in speaking as she did.” Noting that the king had visited her when they were both being treated in a London hospital, the palace said Charles “has remained in the closest contact with his beloved daughter-in-law throughout the past weeks.”

Kate offered a timeline of her medical treatment that eerily echoed that of her father-in-law. At the time her surgery was performed, doctors believed that her condition was noncancerous. The surgery was successful, she said, but in further tests, the doctor found evidence of cancer. They recommended a course of chemotherapy, which she said she had recently begun.

The palace said the king’s cancer was detected after a procedure for an enlarged prostate. While the palace has said he does not have prostate cancer, it has not specified what kind of cancer it is nor his prognosis.

Until Kate’s video, Kensington Palace, where William and Kate have their offices, had released even fewer details about her condition, an information vacuum that contributed to a raft of rumors and conspiracy theories on social media.

British papers found themselves in a difficult position, as courts have ruled that the right to privacy extends to members of the royal family. The Editors’ Code of Practice, under which much of the British press operates, protects all individuals against unjustified intrusion into matters of physical and mental health.

Kate suggested that the family needed a zone of privacy for her to come to terms with her situation and to explain it to her children. The announcement was timed for Friday, a palace official said, because the children had just begun their Easter holiday from school and would not have to face the crush of media coverage — or, presumably, to endure questions about their mother from classmates.

“It has taken me time to recover from major surgery in order to start my treatment,” Kate said. “But, most importantly, it has taken us time to explain everything to George, Charlotte and Louis in a way that is appropriate for them and to reassure them that I am going to be OK.

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

The rumors about Kate’s health began to swirl soon after Kensington Palace announced in January that she would enter the London Clinic, a private hospital, for abdominal surgery and remain there for 10 to 14 days. There were no pictures of her children arriving or leaving the hospital to visit their mother, and only a single shot of William, at the wheel of a car, leaving the hospital.

Four weeks after Kate’s release, William abruptly withdrew from a memorial service for his godfather, King Constantine of Greece, citing a “personal matter,” which accelerated the speculation about Kate on social media.

On Mother’s Day in Britain, Kensington Palace released a photograph of Kate with her three children, taken by William. The goal was to quell the speculation about her, but the photo ignited a new round of conspiracy theories after The Associated Press and other news agencies reported that it had been digitally altered.

Kate apologized for the editing, for which she said she was responsible, chalking it up to an amateur photographer’s innocent desire to improve the image. But it raised questions about how the royal family communicates with the public: Kate has photographed many members of the royal family in private settings, and those photos have often been published by British newspapers.

This week, video footage emerged of William and Kate walking out of a food store near their home in Windsor. The palace, as it has throughout this period, declined to confirm the footage, leading to yet more speculation.

For all the questions that the video left unanswered, royal watchers said Kate’s announcement Friday was a step in the right direction.

“The video message is a welcome intervention and will hopefully do much to dispel the wild rumors and speculation of the last three weeks,” said Ed Owens, a royal historian. “Such transparency is what we need from the royal family if we are to ensure trust is maintained with the public.”

The New York Times News Service