crown prince vs crown princess

crown prince

noun
  • A person designated and raised to become the next king. 

  • A person expected to inherit or take over an enterprise or undertaking once its current manager retires or dies. 

  • A person designated and raised to become the next emperor. 

crown princess

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

  • The wife of a crown prince. 

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