take the secret to the grave

take a/the secret to (one's)/the grave

To not reveal a secret for the duration of one's life. I can't believe that grandma took such a huge family secret to her grave! If Uncle Joe hadn't blurted it out, we'd never have known about it! Oh, Emily is a loyal friend—she would definitely take the secret to the grave.
See also: grave, secret, take
Farlex Dictionary of Idioms.

take the (or your etc.) secret to the grave

die without revealing a secret.
See also: grave, secret, take
Farlex Partner Idioms Dictionary
See also:
  • take a/the secret to (one's)/the grave
  • carry a secret to (one's)/the grave
  • carry a secret to the grave
  • Graves
  • the cat is out of the bag
  • won't breathe a word
  • not breathe a word
  • not breathe a word (of something)
  • in secret
  • pifky