crown princess vs successor

crown princess

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

  • The wife of a crown prince. 

successor

noun
  • A person who inherits a title or office. 

  • The next heir in order or succession. 

  • A person or thing that immediately follows another in holding an office or title. 

  • The integer, ordinal number or cardinal number immediately following another. 

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