
329 S.W.3d 906 (2010)
In re Priscilla TREVINO, Relator.
No. 05-10-01427-CV.
Court of Appeals of Texas, Dallas.
December 14, 2010.
Gary L. Schappaugh, Gary L. Schappaugh, P.C., Mesquite, TX, for Relator.
Julio Trevino, Jr., Jenny Lee Womack, Palmer & Manuel, LLP, Dallas, for Real Party in Interest.
Before Justices O'NEILL, FITZGERALD, and LANG-MIERS.

OPINION
Opinion by Justice LANG-MIERS.
Relator filed this mandamus proceeding after the trial court entered an order granting real party in interest's motion for new trial. We conclude the trial court abused its discretion in doing so and relator has no adequate remedy by appeal. See In re Prudential Ins. Co., 148 S.W.3d 124, 135-36 (Tex.2004) (orig. proceeding); Walker v. Packer, 827 S.W.2d 833, 839-40 (Tex.1992) (orig. proceeding). We therefore conditionally grant the writ of mandamus.
Relator, the paternal aunt of the children in question, filed a suit affecting the parent-child relationship on August 2, 2010. The children's mother is deceased, and the children's father approved the decree appointing relator sole managing conservator. The decree was entered on August 6, 2010. On August 30, 2010, real party in interest, the maternal grandmother of the children, filed a motion for new trial. The trial court granted the motion for new trial on October 6, 2010. Because real party in interest was not a party to the lawsuit, she could not file a motion for new trial after judgment had been entered. Gaines v. Baldwin, 629 S.W.2d 81, 83 (Tex.App.-Dallas 1981, no writ). Moreover, because the court's plenary jurisdiction expired on September 6, 2010, it no longer had jurisdiction to set aside the decree and grant a new trial on its own motion. TEX.R. CIV. P. 329b(f). The trial court's October 6, 2010 order was thus an abuse of discretion for which relator does not have an adequate remedy by appeal. Accordingly, we conditionally grant relator's petition for writ of mandamus. A writ will issue only in the event the trial court fails to vacate its October 6, 2010, "Order Granting Motion for New Trial" and to enter an order denying the motion for new trial.
