Cal. Ins. Code § 10369.5
A disability policy may contain a provision in the form set forth in this section. If the provision also contains the provision set forth in Section 10369.6, there shall be added to its caption the phrase, "* * * expense incurred benefits." The insurer may, at its option, include in this provision a definition of "other valid coverage," approved as to form by the commissioner. The definition shall be limited in subject matter to coverage provided by organizations subject to regulation by insurance law or by insurance authorities of this or any other state of the United States or any province of Canada, or by hospital or medical service organizations, and to any other coverage, the inclusion of which may be approved by the commissioner. In the absence of that definition, the terms shall not include group insurance, automobile medical payments insurance, or coverage provided by hospital or medical service organizations or by union welfare plans or employer or employee benefit organizations. For the purpose of applying this policy provision with respect to any insured, any amount of benefit provided for the insured pursuant to any compulsory benefit statute, including any workers' compensation or employers' liability statute, whether provided by a governmental agency or otherwise, shall in all cases be deemed to be "other valid coverage" of which the insurer has had notice. In applying this provision, no third party liability coverage shall be included as "other valid coverage."
Insurance With Other Insurers: If there is other valid coverage, not with this insurer, providing benefits for the same loss on a provision of service basis or on an expense incurred basis and of which this insurer has not been given written notice prior to the occurrence or commencement of loss, the only liability under any expense incurred coverage of this policy shall be for the proportion of the loss as the amount which would otherwise have been payable under this policy plus the total of the like amounts under all the other valid coverages for the same loss of which this insurer had notice bears to the total like amounts under all valid coverages for the loss, and for the return of the portion of the premiums paid as shall exceed the pro-rata portion for the amount so determined. For the purpose of applying this provision when other coverage is on a provision of service basis, the "like amount" of the other coverage shall be taken as the amount which the services rendered would have cost in the absence of the coverage.
Ca. Ins. Code § 10369.5