King Charles and Sarah Ferguson have “bonded” over heartfelt letters after cancer diagnoses. Charles and the Duchess of York have sent letters of support to each other over their respective cancer announcements, according to a source. Last week, Buckingham Palace announced that the King has been diagnosed with a form of cancer, but the specific type has not been disclosed. The announcement came just over two weeks after the Duchess of York announced that she had been diagnosed with a form of skin cancer. A source said: “The King and Sarah are incredibly fond of one another and now they have bo…