Tom Parker Bowles says his stepfather King Charles is “strong” amid his battle with cancer. The son of Queen Camila, 77, has admitted it’s been a “very worrying” time for the 76-year-old monarch and the rest of the Royal Family since he was diagnosed with the “terrifying disease” in January, but he’s doing all he can and following doctors’ advice. Speaking to PEOPLE magazine, the writer said: “The King is strong. He is doing what he can. He’s following the advice of his doctors. Fingers crossed, touch wood. “It’s a terrifying disease, and when someone close to you gets it in whatever capacity,…