The British newspaper "The Sun" said that the lunch conversation was heart-to-heart, and Kate wanted her to learn from the king how he dealt with his battle against the disease.

A source told the newspaper that Charles and Kate had a lot to discuss during lunch at Windsor Castle, adding: “The King left his lunch feeling very emotional. They are very close and he considers Kate his daughter.”

An informed source told The Telegraph that Kate and Charles feel comfortable with each other as they both suffer from cancer at the same time.

The source added: “The King treats Kate like the daughter he never had.”

Another source added to The Times: “The King has always had a close, warm and unique relationship with the Princess. She has great love and respect for him.”

Princess Kate (42 years old) announced on Friday evening that she had been diagnosed with cancer, the nature of which was not specified.

The wife of the heir to the British throne began preventive chemotherapy.

She received a flood of messages of support from political officials, celebrities and members of the public.