King Charles
A spokesperson for the monarch said they have been in the "closest contact" in recent weeks.
The private members' club has faced scrutiny after its men-only membership list, which reportedly includes judges, MPs and actors, was revealed.
Another reminder not to believe everything you read on the internet.
The Princess of Wales returned home to Windsor last month after spending nearly two weeks in the hospital.
The monarch made the comments during his first meeting with the prime minster this year.
The Duke of Sussex says he immediately arranged to go to the UK after his father called to tell him he had cancer.
The palace said on Monday that the monarch had begun treatment for cancer, days after undergoing surgery.
The Prince of Wales also addressed Kate Middleton's recent surgery and hospital stay.
The monarch is currently still carrying out his constitutional duties after his cancer diagnosis.
A previous announcement of the monarch's enlarged prostate led to a significant increase in searches for the condition on the NHS website.