Crown vs crown prince

Crown

name
  • The sovereign, in a monarchic country. 

  • The government, in a monarchic country. 

  • A Crown attorney. 

crown prince

noun
  • 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. 

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

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