Tex. Fam. Code §102.006
Limitations On Standing

Except as provided by Subsections (b) and (c), if the parent-child relationship between the child and every living parent of the child has been terminated, an original suit may not be filed by: (1) a former parent whose parent-child relationship with the child has been terminated by court order; (2) the father of the child; or (3) a family member or relative by blood, adoption, or marriage of either a former parent whose parent-child relationship has been terminated or of the father of the child.

The limitations on filing suit imposed by this section do not apply to a person who: (1) has a continuing right to possession of or access to the child under an existing court order; or (2) has the consent of the child's managing conservator, guardian, or legal custodian to bring the suit.

The limitations on filing suit imposed by this section do not apply to a relative within the fourth degree of consanguinity of a former parent whose parent-child relationship with the child has been terminated by court order if the relative files an original suit or a suit for modification requesting managing conservatorship of the child not later than the 90th day after the date the parent-child relationship between the child and the parent is terminated in a suit filed by the Department of Family and Protective Services requesting the termination of the parent-child relationship.