23 Pa.C.S. § 3333: Res judicata and estoppel.

The validity of a divorce or annulment decree granted by a court having jurisdiction over the subject matter may not be questioned by a party who was subject to the personal jurisdiction of the court except by direct appeal provided or prescribed by law. A party who sought and obtained a decree, financed or agreed to its procurement, or accepted a property settlement, alimony pendente lite or alimony pursuant to the terms of the decree, or who remarries after the decree, or is guilty of laches, is barred from making a collateral attack upon the validity of the decree unless, by clear and convincing evidence, it is established that fraud by the other party prevented the making of a timely appeal from the divorce or annulment decree.