crown princess vs heiress

crown princess

noun
  • The wife of a crown prince. 

  • The heiress apparent to the throne in a royal or imperial monarchy. 

heiress

noun
  • A woman who has received an inheritance. 

  • A woman who has a right of inheritance or who stands to inherit. 

How often have the words crown princess and heiress occurred in a corpus of books? (source: Google Ngram Viewer )