The Duke and Duchess of Cambridge open a new children's cancer unit.
The Duchess of Cambridge had a chat with 18-year-old Beth Ansell who is a patient at the hospital.
The Prince caught up with Press Packer Alice Marples who interviewed him two years ago for Newsround when she was 10. Alice called him Prince Harry by accident during the interview in 2009!
Both Kate and William took time to talk to the people who waited outside to see them.
Prince William had visited the hospital before - but this was Kate's first visit.
Kate met families who use the cancer hospital and she even accepted a bunch of flowers from the crowd.
Kate met 9-year-old Fabian Bate as he had treatment for leukaemia. The Duchess also said she would post a message on his family's online blog.
The night before the hospital visit Prince William didn't get much sleep as he'd been working for 24 hours in his job as an RAF search and rescue helicopter pilot. But his tiredness didn't stop him joking with patients!
The Duke and Duchess of Cambridge got a tour of the new cancer ward and also met 14-year-old Digby Davidson, who's a patient at the hospital.
The Duke and Duchess of Cambridge opened a new children's cancer ward at the Royal Marsden Hospital in Sutton, south London.