Kate asked for “time, space and privacy” while she is treated for an unspecified type of cancer, which was discovered after her surgery.
“I am well," she said. "I am getting stronger every day by focusing on the things that will help me heal.”
Kate, 42, hadn’t been seen publicly since Christmas until video surfaced this week of her with her husband, Prince William, heir to the throne, walking from a farm shop near their Windsor home.
The news is another jolt for the royal family since the announcement last month that King Charles III was being treated for an unspecified type of cancer that was discovered while undergoing a procedure for a benign enlarged prostate.
Charles said he is “so proud of Catherine for her courage in speaking as she did,” according to a statement released by Buckingham Palace. He had remained in the “closest contact with his beloved daughter-in-law" in the past weeks.
Kensington Palace had given little detail about Kate’s condition beyond saying it wasn’t cancer-related, the surgery was successful and recuperation would keep the princess away from public duties until April. Kate said it had been thought that her condition was non-cancerous until tests revealed the diagnosis.
“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," she said.
Kate said it had taken her time to recover from major surgery before starting preventative treatment, which she said was in the early stages.
“Preventive chemotherapy after surgery is given to reduce the risk of the cancer coming back in the future — a bit like mopping a floor with bleach when you’ve spilt something on it, chemotherapy kills any spilt cells,” said Professor Andrew Beggs, a senior clinical fellow at the University of Birmingham.
Kate said it has been “an incredibly tough couple of months” for her family. She said it had taken time to tell her three children Prince George, Princess Charlotte and Prince Louis in a way “appropriate for them” and reassure them she will be OK.
The news comes after the start of the Easter holidays, which will shield the children from media coverage of the news.
British Prime Minister Rishi Sunak said in a statement that Kate “has shown tremendous bravery.” He added: “In recent weeks she has been subjected to intense scrutiny and has been unfairly treated by certain sections of the media around the world and on social media.”
Keir Starmer, leader of the main opposition Labour Party, also sent his best wishes to the princess at this “distressing time.”
“We are incredibly sad to hear of the news,” said White House Press Secretary Karine Jean-Pierre, who opened her briefing with reporters moments after news of cancer treatment broke. “We are taking this in, this terrible news, as all of you are.”
Charles, 75, has withdrawn from public duties while he has cancer treatment, though he's appeared frequently in photos carrying on meetings with government officials and dignitaries and was even seen going to church.
Kate, on the other hand, had been out of view instead of appearing at charity events and promoting causes such as early childhood, leading to weeks of speculation and gossip. Attempts to put rumors to bed by releasing a photo of her on Mother's Day in the U.K. surrounded by her three smiling children backfired when The Associated Press and other news agencies retracted the image because it had been manipulated.
Kate issued a statement the next day acknowledging she liked to "experiment with editing" and apologizing for "any confusion" the photo had caused. But that did little to quell the speculation.
Even the footage published by The Sun and TMZ that appeared to show Kate and William shopping sparked a new flurry of rumor-mongering, with some armchair sleuths refusing to believe the video showed Kate at all.
Earlier this week, a British privacy watchdog said it was investigating a report that staff at the private London hospital where she was treated tried to snoop on her medical records while she was a patient for abdominal surgery.
The former Kate Middleton, who married William in a fairy-tale wedding in 2011, has boosted the popularity and appeal of the British monarchy worldwide more than any royal since Princess Diana.
The princess is the oldest of three children brought up in a well-to-do neighborhood in Berkshire, west of London. The Middletons have no aristocratic background, and the British press often referred to Kate as a “commoner” marrying into royalty.
Kate attended the private girls’ school Marlborough College and then University of St. Andrews in Scotland, where she met William around 2001. Friends and housemates at first, their relationship came to be in the public eye when they were pictured together on a skiing holiday in Switzerland in 2004.
Kate graduated in 2005 with a degree in art history and a budding relationship with the prince.