The princess of Wales is undergoing cancer treatment.
Catherine says it was a "huge shock" after an "incredibly tough couple of months".
But in a positive message, she says is well and getting stronger every day.
Details of the cancer have not been disclosed, but Kensington Palace says it is confident the Princess will make a full recovery.
The Princess's statement explains that when she had abdominal surgery in January, it was not known that there was any cancer.
She says however, tests after the operation found cancer had been present and her medical team therefore advised that she should undergo a course of preventative chemotherapy and she is in the early stages of that treatment.
The chemotherapy treatment began in late February.
The palace says it will not be sharing any further private medical information, including the type of cancer.
The princess, 42, says she was thinking of all those who have been affected by cancer, adding for everyone facing this disease, in whatever form, please do not lose faith or hope and you are not alone.
Catherine says recovery from her surgery in January, for a condition which has not been revealed, had taken time and the priority was now reassuring her family.
She says the family now needs some time, space and privacy.
The King and Queen had been informed of the news about the Princess's health prior to the announcement - and King Charles himself has also been undergoing treatment for cancer.
Source: BBC news
