King Charles has felt “frustrated” amid his cancer treatment. The 75-year-old monarch was diagnosed with cancer earlier this year, and Peter Phillips – who is the the only son of Princess Anne and her first husband Captain Mark Phillips – has now revealed how Charles is coping with his treatment. Speaking to Sky News Australia, Peter shared: “He’s in good spirits. “I think, ultimately, he’s hugely frustrated. He’s frustrated that he can’t get on and do everything that he wants to be able to do. “But he is very pragmatic (and) he understands that there’s a period of time that he really needs to…