私下知道，知晓（内情）
to be told information that is not told to many people
I was never privy to conversations between top management. 高层管理者之间的对话我从不知情。
She relied on support from the close circle of friends who were privy to her diagnosis.
Computerized records mean that your doctor is privy to all your medical details.
In that role, he was privy to some of the nation's most important military information.
There has been an investigation, but I'm not privy to its findings.
See also: privy adjective