[MILLICENT . A manuscript narrating the foundation of Wigmore Abbey records that “Milesaunt filia --- comitis Derbeyæ” was the first wife of “domini Rogeri”[245]. This has not been corroborated from other primary sources, but, if it is correct, her father must have been William 3rd Earl. m as his first wife, ROGER de Mortimer, son of HUGH de Mortimer & his wife Matilda Meschin of Skipton-in-Craven [Chester] (-before 19 Aug 1214, bur Wigmore).]

http://fmg.ac/Projects/MedLands/ENGLISH%20NOBILITY%20MEDIEVAL1.htm#MillicentDerbyMRogerMortimer