By Russell Myers The King and Fergie have been supporting each other over their cancer battles, it can be revealed. Charles and Sarah Ferguson have exchanged heartfelt letters with one another following their diagnoses of the cruel disease. The 75-year-old monarch was the first to reach out to the Duchess of York after she was diagnosed with breast cancer last year. Charles wrote to Fergie, 64, again when shortly after Christmas she was dealt another devastating blow and diagnosed with skin cancer. The Duchess has since written to the King to express her best wishes and solidarity with the Kin…