The Princess of Wales has said she is in the early stages of chemotherapy.
In a video statement, Catherine said the cancer diagnosis was a "huge shock".
Details of the cancer have not been disclosed, but according to BBC, Kensington Palace has said it is confident the princess will make a full recovery.
In the video, the princess says that when she had abdominal surgery in January, it was not known that there was any cancer.
It was only following the operation that tests showed she had cancer.
She says she is in the early stages of treatment and her priority is now her family. Together with William, she has explained to their three children George, Charlotte and Louis that she was going to be ok.
Catherine added that her family now needed some time, space and privacy.
The video of the princess was filmed on Wednesday by BBC Studios, the production arm of the BBC.
The 42-year-old has not been seen in public since attending a Christmas Day church service, fuelling speculation about her health, particularly online.
Last week she apologised and admitted to editing an official portrait of her released by Kensington Palace on Mother's Day, after AFP and other agencies withdrew the image.
Last month, Buckingham Palace announced that Catherine's father-in-law - King Charles III - had also been diagnosed with a form of cancer.
UK Prime Minister Rishi Sunak later reassured the public that the cancer diagnosis for the 75-year-old king was made early.