regrettably vs ruthfully

regrettably

adv
  • In a manner inspiring or deserving regret. 

ruthfully

adv
  • In a manner that causes pity; piteously. 

  • Sorrowfully, ruefully. 

  • Compassionately; mercifully. 

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