An insurer is not required to contribute to a different insurer’s defense costs if that insurer assumed the defense voluntarily. Here, Federal had issued an umbrella policy which did not attach if there was an unexhausted primary insurance policy covering the same loss. Truck had issued such a policy and was brought into the defense late by the insured. As a result, Federal sued to force Truck to reimburse Federal for defense costs it had incurred before Truck’s policy was discovered. This decision holds that Federal was not entitled to reimbursement because its umbrella policy did not require it to defend the insured, but instead provided that Federal could associate in on the defense at its own election and expense. When it incurred defense costs under that policy language, it did so as a volunteer and could not recoup those costs from Truck. Moreover, the case holds that in not revealing that it paid the defense costs as a volunteer, Federal committed an extrinsic fraud which allowed Truck to escape its agreement which had settled prior litigation with Federal over the same defense costs.