let in on

US /let ɪn ɑːn/
UK /let ɪn ɑːn/
"let in on" picture
1.

посвятить в, дать знать

to allow someone to share a secret or to know something that is not known by many people

:
They finally let me in on their plans for the surprise party.
Они наконец-то посвятили меня в свои планы на вечеринку-сюрприз.
She refused to let him in on the secret.
Она отказалась посвящать его в тайну.