On February 19, 1948, Duff Cooper, the former British ambassador to France and a noted appraiser of women, went with his wife, Lady Diana, to a luncheon at Buckingham Palace with the King, Queen, and their two daughters, the Princesses Elizabeth and Margaret Rose (as Margaret was then called). Afterward he wrote in his diary, “We enjoyed it enormously. Conversation never flagged and was really amusing. Margaret Rose is a most attractive girl—lovely skin, lovely eyes, lovely mouth, very sure of herself and full of humour.” He added presciently, “She might get into trouble before she’s finished.”
It was not long before she did. The Princess, then 17, was already in love with one of her father’s courtiers, a love that would blaze across headlines and almost cause a constitutional…