The correct answer to the question "Who is the Duchess of Cornwall?" is option 2: Camilla. Camilla, Duchess of Cornwall, is the wife of Prince Charles, the heir to the British throne. She became the Duchess of Cornwall when she married Prince Charles in 2005. It is important to note that Diana, Princess of Wales, was also a prominent figure in the British royal family, but she held the title of Princess of Wales, not Duchess of Cornwall. Option 1, Diana, is therefore not the answer to this question. Similarly, options 3 and 4, Anne and Margaret, do not hold the title of Duchess of Cornwall and therefore are also incorrect.