See Peter Bartrum, https://www.geni.com/documents/view?doc_id=6000000173393022984 (April 19, 2023; Anne Brannen, curator)

Please see Peter Bartrum: https://www.geni.com/documents/view?doc_id=6000000173392989825. He charts Cadwgan ap Madog as Gwenllian's second husband but indicates his doubt. (Steven Ferry, May 8, 2022.)

Please see Darrell Wolcott: Cynwrig ap Rhiwallon; http://www.ancientwalesstudies.org/id293.html (Steven Ferry, May 8, 2022.)

Please see Darrell Wolcott: The Children of Owain Gwynedd; http://www.ancientwalesstudies.org/id302.html [ NOTE: besides the Gwenllian born to Owain Gwynedd and Gladys ferch Llywarch, Bartum charts an illegitimate Gwenllian, born to an unknown mistress, and married to 1) Hwfa ap Cynwrig and 2) Cadwgan of Nannau.(https://www.geni.com/documents/view?doc_id=6000000173392989825) Wolcott charts two illegitimate Gwenllians, 1) born c.1125, married to Cadwgan, and 2) born c. 1135 and married to Hwfa. He bases this on the dating of Gruffudd ap Cadwgan to c.1155, based on his marriage to Gwenllian/Angharad ferch Dafydd ap Owain Gwynedd of c. 1170. This would preclude a Gwenllian, married to Cadwgan and having son Gruffudd at c. 1155, from having a daughter with Hwfa in c. 1150 (Angharad ferch Hwfa.) However, if these dates do not hold up, there is the possibility that a Gwenllian born c,1125 could have been married first to Cadwgan, having his children, and then marrying Hwfa and having Angharad.] (Steven Ferry, September 11, 2022.)

Please see Darrell Wolcott: King Llewelyn ap Iorwerth and Ednyfed Fychan; http://www.ancientwalesstudies.org/id308.html (Steven Ferry, November 25, 2022.)