deep, dark secret – російський переклад

скелет в шкафу (A piece of information that is extremely private and confidential, usually implied to be embarrassing, incriminating, or shameful: I've carried my fear of clowns as a deep, dark secret for many years now. Many saw her as a perfect candidate, but no one could have known she had a deep, dark secret from her past. Bullfinch)

Англійський тезаурус