Camilla is “deeply unhappy”, according to insiders, as the Queen is understood to face a constant battle with King Charles. Despite being diagnosed with a form of cancer earlier this year, the monarch continues to perform a packed schedule of royal engagements. This includes an upcoming gruelling overseas tour to Australia, which is being planned for October. Earlier this week, King Charles, 75, began his summer holiday at Balmoral Castle in Scotland for a well-deserved break. He took part in a traditional Balmoral welcoming ceremony on Monday. However, the following day King Charles flew hund…