King George VI, 43, was prone to bashfulness and insecurity. Thrust on to the throne in December 1936 when his older brother abdicated in order to marry the twice-divorced American Wallis Simpson, he felt ill-prepared for his role. He suffered from a stutter, which made public speaking difficult. And he suspected he came up short in comparison with the former king, known after the abdication as the Duke of Windsor. "Especially in America," Diane Kunz, a historian who has taught at Yale, explains to the BBC, "the Duke of Windsor was considered the superstar royal, a popular modern guy, while...