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 “well and getting stronger every day.”

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 disclosure follows the announcement by Buckingham in February that King Charles III was diagnosed with cancer. The palace has not revealed what type of cancer he has, only that he is receiving treatment.

Catherine was last pictured on the weekend, smiling and walking next to Prince William during a visit to a farm shop in Windsor. The Washington Post could not verify when the video was recorded. The palace did not deny that the video was authentic.

Pietsch reported from Washington.