If you let someone in on something that is a secret from most people, you allow them to know about it.
I’m going to let you in on a little secret...
PHRASAL VERB : V n P P n
If you let someone in on something that is a secret from most people, you allow them to know about it.
I’m going to let you in on a little secret...
PHRASAL VERB : V n P P n
Collins COBUILD Advanced Learner's English Dictionary. Английский словарь Коллинз COBUILD для изучающих язык на продвинутом уровне. 2006