From an interview in the Telegraph, inter alia:
What is he reading? “Ah, some old Greek writer, a historiographer, Diodorus Siculus. I’m only reading him because he has the best details on Alexander the Great’s father, Philip II of Macedon, who was a very, very fascinating person.” He considers a moment, then gives forth a miniature Herzogism: “You can’t get wilder soap opera than reading Diodorus Siculus on Alexander the Great’s father.”