Rule 959 There is no privilege under this article as to a communication relevant to an issue concerning the intention or competence of a client executing an at…

When a lawyer signs a document as a witness (called an "attesting witness"), they cannot use attorney-client privilege to hide communications about that document. This applies to questions about whether the client understood what they were signing or truly meant to sign it.

For example, if a lawyer witnesses a client signing a will and there is later a dispute about whether the client was mentally able to make a will, the lawyer can be required to share what they know. The lawyer cannot refuse to answer by claiming the information is confidential.