The Princess of Wales, 42, underwent surgery in January. The palace did not disclose details at the time but said the procedure was planned and her condition was "not cancer-related". (source: bbc.com)
Kate Middleton's recent video message on the Official Royal Channel says that tests carried out after the operation found cancer had been present.
Kensington Palace has not said what type of cancer she has.
A spokesperson said: "We will not be sharing any further private medical information. The princess has a right to medical privacy as we all do." (source: bbc.com)
Catherine said her medical team advised she should undergo "preventative chemotherapy" and she is in the early stages of this treatment. (source: the dailymail.co.uk)
Chemotherapy is a catch-all term for medication to kill cancer cells - it can be given via a drip or in pill form. Preventive chemotherapy after surgery is given to reduce the risk of the cancer coming back in the future. How much you need and how often depends on the type of cancer and how it is growing. (source: bbc.com)
How many people get cancer?
In the UK, one in two people develop some kind of cancer during their lifetime. (source: bbc.com)
There are more than 200 different types of cancer - the most common ones in the UK are breast, lung, prostate, and bowel, according to the NHS UK website.
In her emotional video, the Princess of Wales underlined that she is well and that now more than ever Royals need time and privacy as a family because her three kids are also there and must not suffer from this unfortunate but curable diagnosis.