What is the test for disqualification of an attorney who has previously represented the same client at the same time?

Next, we address the conflict of interest issue. Conflicts of interest can arise when an attorney seeks to represent a client with interests that are potentially adverse to a former client of the attorney. (In re Charlisse C. (2008) 45 Cal.4th 145, 159.) When successive representation is an issue, "'the chief fiduciary value jeopardized is that of client confidentiality.' [Citation.]" (Ibid.) In order for an attorney to be disqualified due to a conflict based on successive representation, it must be shown that there is a substantial relationship between the subject matter of the previous case and the current case. (Flatt v. Superior Court (1994) 9 Cal.4th 275, 283-284.)