Kate Middleton announced her news in an emotional interview, where she told others who are battling the illness, "you are not alone".
In the video, Kate spoke about the "huge shock" at her diagnosis, and that her family have been through an "incredibly tough couple of months".
She also stated that she maintains a positive frame of mind for her recovery, having undergone a course of "preventative chemotherapy" in late February. The Princess of Wales said that she is "well and getting stronger every day".
"In January, I underwent major abdominal surgery in London and at the time, it was thought that my condition was non-cancerous", Kate said in the video. "The surgery was successful. However, tests after the operation found cancer had been present. My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment.
"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. As you can imagine, this has taken time".
The future queen also added, "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 in a way that is appropriate for them, and to reassure them that I am going to be OK.
"As I have said to them; I am well and getting stronger every day by focusing on the things that will help me heal; in my mind, body and spirits".
This announcement is likely to end weeks of major speculation, and conspiracy theories on social media about the whereabouts and health of the Princess of Wales.
Her length of treatment remains unknown, but it is understood that Kate may attend some public events, as and when she feels able to, subject to medical advice.
King Charles who is also being treated for cancer, has been told about his daughter-in-law's health, while Kate and William's three children have began their Easter school holidays, taking advantage of the opportunity to shield them from the media coverage of her mother's health.
