King Charles is “extremely concerned” about Princess Kate amid her health troubles, according to a royal source. The Princess of Wales and King Charles are currently undergoing treatment for undisclosed forms of cancer. Although the King has always been close with his “beloved” daughter-in-law, a source has said that Charles is willing to do “anything he can do” to support her. Robert Hardman, author of Charles III: New King, New Court, said: “It’s very clear that he [King Charles] is extremely concerned about her [Kate]. “I think he wants to make sure as much as he can that if there’s anythin…