LOL!

Well, seriously, I'd say that if you're a moderator and having an off-board discussion over an issue involving the board, that should probably be between the two of you. But I'd probably make it clear to them that I was discussing it under those conditions, and then if they copied someone else on the board on your discussion, you'd have the right to take action against them.

You don't go into more detail or say who the third party is a cyber friend OF, so that's all I could tell you...