About Gwladys "Ddu" verch Llewelyn
From Medlands:

http://fmg.ac/Projects/MedLands/WALES.htm#Gwladusdied1251

GWLADUS Ddu . The Annals of Dunstable record that “Reginaldus frater eius” married “Leulini Regis Walliæ…filiam” in 1216[277]. Henry III King of England granted protection to "Gwladosa filia…[L.] principis [Norwallie] que fuit uxor Reginaldi de Brausa" dated [May] 1229, issued at the same time as letters of protection to her brother David[278]. Henry III King of England granted safe passage to "David filium L. principis Norwallier in veniendo ad regem ad faciendum ei homagium suum, et sororem ipsius David" dated 5 Sep 1229[279]. It is likely that this unnamed sister of David was Gwladus, coming to England with her brother before her second marriage. The Annals of Worcester record that “Radulphus de Mortuomari” married “filiam Lewelini, conjugem quondam Reginaldi de Breusa” in 1230[280]. A manuscript narrating the foundation of Wigmore Abbey records that “Radulphus” married “Lewelinus princeps…Gwladusam Duy filiam suam”, who brought her husband “omnibus terries de Kery et Kedewyn”[281]. The Annales Cambriæ record the death in 1251 of "Gladus filia domini Lewelini" at Windsor[282]. m firstly as his second wife, REYNOLD de Briouse, son of WILLIAM [III] de Briouse & his wife Mathilde de Saint-Valéry Dame de la Haye . He succeeded in 1215 as Lord of Abergavenny[283]. m secondly RALPH de Mortimer of Wigmore, son of ROGER de Mortimer & his wife Isabel de Ferrers .

http://fmg.ac/Projects/MedLands/ENGLISH%20NOBILITY%20MEDIEVAL2.htm

RALPH Mortimer of Wigmore . A manuscript narrating the foundation of Wigmore Abbey records that “Radulphus frater eius” succeeded on the death of “Hugo”, adding that he was born from his father´s second marriage, built “duo castra…Kevencles et Knoclas”, died “VIII Id Aug 1247” and was buried “in abbathia de Wygemore”[286]. "Ralph de Mortimer" made a fine "for having seisin of the lands formerly of Hugh de Mortimer, his brother", dated [Nov] 1227[287]. The Annales Cambriæ record the death in 1246 of "Radulphus de Mortuo Mari"[288]. m as her second husband, GWLADUS Ddu , widow of REYNOLD de Briouse, illegitimate daughter of LLYWELLYN ap Iorwerth Fawr Prince of Wales & his mistress --- . The Annals of Worcester record that “Radulphus de Mortuomari” married “filiam Lewelini, conjugem quondam Reginaldi de Breusa” in 1230[289]. A manuscript narrating the foundation of Wigmore Abbey records that “Radulphus” married “Lewelinus princeps…Gwladusam Duy filiam suam”, who brought her husband “omnibus terries de Kery et Kedewyn”[290]. Ralph & his wife had five children

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ not listed at FMG http://fmg.ac/Projects/MedLands/WALES.htm#Gruffydddied1244B [This statement is refuted by the above] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

of Caernarvonshire, Cymru. Also called "the Black" because of her dark coloring.
Some Corrections and Additions to the Complete Peerage, www.uk-genealogy.org.uk/cp/index.shtml, Page: I:22: Not a daughter of Joan, but of Llewellyn's mistress Tangwystl.

1st husband Reginald De Braose 2nd husband Ralph De Mortimer

Burke's Guide to the Royal family states the 2nd husband was Roger De Mortimer, yet the IGI states that it was Ralph, as does Sanders. The death date of Ralph matches the death date that Burke's Guide gives for Roger, so Ralph will be the accepted husband. The IGI and Cokayne also state that Ralph married Gwladus Ddu Llewelyn.

Foster, Cokayne and Sanders has her mother as Princess Joan, daughter of King John, the other wife of Llewelyn.