a word

[Tdol]

An éminence grise would definitely have a confidential secretary.

[SlickVic9000]

(Not a Teacher)

I've never heard "confidential" used to describe a person. "Discreet" is the word I think you're looking for. It indicates someone who knows how to keep a secret.

[Rover_KE]

(Not a Teacher)

I've never heard "confidential" used to describe a person.

Besides confidential secretary there's also confidential informant.

And journalists have their confidential sources.

Rover