In general, someone need not be a current client in order for the attorney-client privilege to apply. All that’s typically required is that the parties had an attorney-client relationship when the communications in question were made. In fact, the privilege can apply even where the parties never actually became attorney and client.
Keeping in mind that the law can vary someone from one court to another, read on for general principles about the attorney-client privilege and people who aren't currently clients. For more information, see The Attorney-Client Privilege
End of relationship. The attorney-client privilege is permanent. The client can continue to assert it, and the lawyer must assert it, into perpetuity. That’s true even after the attorney and client's relationship has concluded. (United States v. White, 970 F.2d 328 (7th Cir. 1992).)
Death. The attorney-client privilege survives not only the attorney-client relationship, but also the client’s life. A lawyer cannot divulge confidential communications between his client and him ever, even after the client dies. (Swidler & Berlin v. United States, 524 U.S. 399 (1998).) The theory is, in part, that some people might not be completely candid with their attorneys if they thought that what they said could ever become public.
Preliminary communications. Generally, someone accused of a crime can candidly discuss her legal situation with a prospective lawyer without fear of disclosure. Preliminary communications between a would-be client and a lawyer are typically subject to the privilege, meaning that the lawyer can’t disclose what the defendant revealed in confidence even if the lawyer never ends up representing the defendant. (In re Auclair, 961 F.2d 65 (5th Cir. 1992).) (To be sure, though, defendants are well advised to confirm with a prospective lawyer that the privilege applies.)