20 CFR § 404.728 - Evidence a marriage has ended.
(a) When evidence is needed that a marriage has ended. If you apply for benefits as the insured person's divorced wife or divorced husband, you will be asked for evidence of your divorce. If you are the insured person's widow or divorced wife who had remarried but that husband died, we will ask you for evidence of his death. We may ask for evidence that a previous marriage you or the insured person had was ended before you married each other if this is needed to show the latter marriage was valid. If you apply for benefits as an unmarried person and you had a marriage which was annulled, we will ask for evidence of the annulment. We will ask for the evidence described in this section.
(b) Preferred evidence. Preferred evidence a marriage has ended is -
(1) A certified copy of the decree of divorce or annulment; or
(c) Other evidence a marriage has ended. If you cannot obtain preferred evidence the marriage has ended, we will ask you to explain why and to give us other convincing evidence the marriage has ended.