let (one) in on (something)(redirected from let him in on)
let (one) in on (something)
To give one information that is private or not widely known, or to include one in something. All right, I'll let you in on what’s really going on here—we're planning a surprise party for Carla. I can't believe Tim let me in on the special offer he got.
let in on
Allow someone to know about or participate in something, as in I'm going to let you in on a little secret. This idiom was first recorded in 1904.
let (someone) in on
1. To reveal (a secret) to someone: They finally let me in on their plans.
2. To allow someone to participate in (something).