20 CFR § 404.346 - Your relationship as wife, husband, widow, or widower based upon a deemed valid marriage.
(a) General. If your relationship as the insured's wife, husband, widow, or widower cannot be established under State law as explained in § 404.345, you may be eligible for benefits based upon a deemed valid marriage. You will be deemed to be the wife, husband, widow, or widower of the insured if, in good faith, you went through a marriage ceremony with the insured that would have resulted in a valid marriage except for a legal impediment. A legal impediment includes only an impediment which results because a previous marriage had not ended at the time of the ceremony or because there was a defect in the procedure followed in connection with the intended marriage. For example, a defect in the procedure may be found where a marriage was performed through a religious ceremony in a country that requires a civil ceremony for a valid marriage. Good faith means that at the time of the ceremony you did not know that a legal impediment existed, or if you did know, you thought that it would not prevent a valid marriage.
(b) Entitlement based upon a deemed valid marriage. To be entitled to benefits as a wife, husband, widow or widower as the result of a deemed valid marriage, you and the insured must have been living in the same household (see § 404.347) at the time the insured died or, if the insured is living, at the time you apply for benefits. However, a marriage that had been deemed valid, shall continue to be deemed valid if the insured individual and the person entitled to benefits as the wife or husband of the insured individual are no longer living in the same household at the time of death of the insured individual.
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