Tex. Family Code § 6.201: CONSANGUINITY.

A marriage is void if one party to the marriage is related to the other as:

(1) an ancestor or descendant, by blood or adoption;

(2) a brother or sister, of the whole or half blood or by adoption;

(3) a parent's brother or sister, of the whole or half blood or by adoption; or

(4) a son or daughter of a brother or sister, of the whole or half blood or by adoption.

Added by Acts 1997, 75th Leg., ch. 7, Sec. 1, eff. April 17, 1997.