INSURANCE WITH OTHER INSURERS: If this insurer has not been given written notice before the occurrence or commencement of loss that the insured under this policy has other valid coverage, not with this insurer, and that other valid coverage provides benefits for the same loss on other than an expense incurred basis, the only liability for the benefits under this policy is for the proportion of the indemnities otherwise provided under this policy for the loss as the like indemnities of which the insurer had notice, including the indemnities under this policy, bear to the total amount of all like indemnities for the loss, and for the return of the portion of the premium paid that exceeds the pro rata portion for the indemnities determined under this provision.
MCL 500.3440