Definition
To reveal a secret to someone, which was previously kept from others.
告訴某人一個秘密
Can I let you in on a little secret?
我可以告訴你一個小秘密嗎？
She decided to let her best friend in on her plans.
她決定向她的好朋友透露她的計劃。
They trusted me and let me in on the secret stage of the project.
他們信任我，並讓我參與了項目的秘密階段。