The bond between both King Charles and Princess Catherine has grown stronger as the royals face separate cancer diagnoses.

Royal biographer Sally Bedell Smith spoke exclusively to PEOPLE about the growing bond between the King and the Princess.

“He has always had a very good bond with her. I don’t think it is presumptuous to say that she is like the daughter he never had,” she said.

“He shares with William an impulse to protect her. They are in this together, Kate and the King.”

According to Buckingham Palace, King Charles was “so proud of Catherine for her courage in speaking as she did" following her emotional cancer reveal.