King Charles is understood to be “a little frustrated” about his cancer diagnosis impacting his plans, Palace sources have claimed. The 75-year-old monarch, whose diagnosis of cancer was announced by Buckingham Palace on Monday, is back at Sandringham after staying the night at Clarence House. He travelled to Clarence House to begin his medical treatment schedule and will continue his state duties from home, supported by Queen Camilla. A Palace source said: “He’s on his usual good form in every way, just a little frustrated that his condition has affected not just his own plans but impacted on…