What is Princess Diana's name... princess of...?

When she was born, as the daughter of a viscount, she was called the Hon Diana Frances Spencer, and when her father inherited the earldom she became Lady Diana Frances Spencer: she was born an aristocrat but a non-Royal and therefore a commoner.

When she married Prince Charles, she was called Her Royal Highness Diana, Princess of Wales.

When she divorced Prince Charles, she became Diana, Princess of Wales.