Catherine, the Princess of Wales, has been diagnosed with cancer, the BBC reported.
She is now in the "early stages" of chemotherapy.
"I'm fine... getting stronger," Kate said in the first comment since the diagnosis, asking the public for "time, space and privacy."
The British princess said the discovery of the cancer, after a successful abdominal operation in January, was a "huge shock".
The White House wished Catherine "a full recovery following the terrible news of her diagnosis."
"We have all just heard the terrible news. Our thoughts are with the Duchess of Cambridge and her family," said press secretary Karin Jean-Pierre.
British Prime Minister Rishi Sunak wished Princess Kate a "full and speedy" recovery. /BGNES
