He [William de Briouze] m. 2ndly, 1215, Gwladus Du, daughter of Llewelyn ap Iorwerth, Prince of North Wales, by his 2nd wife Joan, illegitimate daughter of King John. He d. between 5 May 1227 and 9 June 1228. His widow m. 2ndly, Ralph de Mortimer, of Wigmore, who d. 6 Aug 1246, and was buried at Wigmore Abbey. She d. at Windsor in 1251. [Complete Peerage I:22]
NOTE: The identity of Gwladus's mother is still a matter of debate. There is no clear contemporary evidence that her mother was Joan, and a daughter of Llewelyn and Joan could not have been aged more than about 9 in 1215. The only direct statements appear to come some centuries later. One strand of the later tradition does identify Gwladus's mother as Joan, but another says she was Llewelyn's mistress Tangwystl.
[This question has been discussed by - among many others - Stewart Baldwin, Rosie Bevan, Ken Finton, Todd Farmerie, John P. Ravilious, Paul Reed, Douglas Richardson, Henry Sutliff, Nat Taylor and Brad Verity.] [Some Corrections and Additions to CP]
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Let me make one final general observation. There was a definite and timely reason that Reginald de Broase married Gwladys Ddu in 1215. His brother Giles, Bishop of Hereford, rebelled as soon as he received a royal grant of 'his' patrimony and joined Llywelyn (as leader of the Welsh forces) in general rebellion against John (remember that this was also about the time the North of England, etc., rebelled against John). Reginald immediately joined his brother in marching on their patrimony in the Marches to secure it by force. To cement their alliance (Giles being a bishop and all), Reginald was married to a daughter of Prince Llywelyn. Her name happened to be Gwladys, the dark eyed.
I would find it EXTRAORDINARILY coincidental if Gwladys just happened to be BARELY age twelve in 1215, when it was found expedient to marry her to Reginald. He was older, already experienced in the art of war and the ability to lead men. His elder deceased brother William was already father of four sons held as hostages by King John.
I would be utterly amazed if we found that Gwladys was aged twelve in 1215. The cause of their marriage was not (as far as we know) a prearranged marriage contract that happened to coincide with political expediency--the marriage was a RESULT of the political events that occurred in 1215.
After Reginald de Braose betrayed Llywelyn and became King John's man in 1217 [to give homage, one had to be in the actual presence of the King], and his nephew John de Braose was released in 1218, Llywelyn found a ready ally in the younger John, who was attempting to get his rightful inheritance from Reginald (who was in possession of most of it), in 1218, Llywelyn, out of political expediency, married his daughter Margared to this John.
Thus, if the marriage between Gwladys and Reginald was the result of political events, and they had not been heatedly awaiting her birthday so that they could be wed in a full and legal manner that would be permanent--rather than something that could be easily broken (or at least broken with some effort and complicity)--I would conclude it is most likely that Gwladys was actually older than twelve years old in 1215. Does that seem reasonable? [Paul C Reed, 30 Nov 2001, soc.genealogy.medieval]