Catherine, the Princess of Wales, announced that she has been diagnosed with cancer and is currently receiving chemotherapy.
Speculation about the princess' welfare and whereabouts has been rife on social media since the prominent royal underwent abdominal surgery at a private London hospital in January.
She has not been seen in public since Christmas.
In a video message released on Friday, she said the diagnosis "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".
"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," the princess added.
“I am well," she said. "I am getting stronger every day by focusing on the things that will help me heal".
The princess, 42, who is also still known as Kate Middleton, asked for "time, space, and privacy" while she is treated for an unspecified type of cancer, which was discovered after her surgery.
Kate said it had been thought that her condition was non-cancerous until tests revealed the diagnosis.
Speculation about Kate's wherabouts
Kensington Palace had so far given little detail about the princess' condition beyond saying it wasn’t cancer-related, the surgery was successful, and recuperation would keep the princess away from public duties until April.
In a statement released on Friday, British prime minister Rishi Sunak said the Princess of Wales had "shown tremendous bravery".
He added: "In recent weeks she has been subjected to intense scrutiny and has been unfairly treated by certain sections of the media around the world and on social media".
The announcement of her condition comes as her father-in-law King Charles III continues his course of treatment for an undisclosed cancer.
The King broke centuries of royal tradition in February to disclose his diagnosis after cancer was discovered after treatment for an enlarged prostate.
While the 75-year-old monarch has withdrawn from public duties for the time being, he has appeared frequently in photos carrying on meetings with government officials and dignitaries, and was even seen attending church.
Kate, on the other hand, has completely withdrawn from public view, sparking weeks of feverish speculation and online gossip.
Attempts to satisfy an appetite for updates backfired when a Mother's Day portrait of the princess with her three children George, Charlotte, and Louis was rejected by the Associated Press and other news agencies after it was found the image had been manipulated.
