Neb. Rev. Stat. § 42-103: Neb. Rev. Stat. § 42-103

Marriages are void (1) when either party has a husband or wife living at the time of the marriage, (2) when either party, at the time of marriage, is mentally incompetent to enter into the marriage relation, and (3) when the parties are related to each other as parent and child, grandparent and grandchild, brother and sister of half as well as whole blood, first cousins when of whole blood, uncle and niece, and aunt and nephew. This subdivision extends to children and relatives born out of wedlock as well as those born in wedlock.