Sec. 154.009. RETROACTIVE CHILD SUPPORT. (a) The court may order a parent to pay retroactive child support if the parent:
(1) has not previously been ordered to pay support for the child; and
(2) was not a party to a suit in which support was ordered.
(b) In ordering retroactive child support, the court shall apply the child support guidelines provided by this chapter.
(c) Unless the Title IV-D agency is a party to an agreement concerning support or purporting to settle past, present, or future support obligations by prepayment or otherwise, an agreement between the parties does not reduce or terminate retroactive support that the agency may request.
(d) Notwithstanding Subsection (a), the court may order a parent subject to a previous child support order to pay retroactive child support if:
(1) the previous child support order terminated as a result of the marriage or remarriage of the child’s parents;
(2) the child’s parents separated after the marriage or remarriage; and
(3) a new child support order is sought after the date of the separation.
(e) In rendering an order under Subsection (d), the court may order retroactive child support back to the date of the separation of the child’s parents.