Cawley gives the birth of Dafydd, son of Gruffydd and Senena, as 1235. 
Other genealogies estimate his birth year as 1230 or 1238.
He was the son of Gruffudd ap Llywelyn "Mawr" ab Iorwerth and Senena ferch Caradog. He was of the tribe of Gruffudd ap Cynan.
Cawley states that Gruffydd married Senena. Wikipedia adds that Senana was possibly a daughter of Caradoc ap Thomas of Anglesey.  Boyer refers to her as Senena ferch Caradog  and addresses no ancestry before Caradog. 
Henry III King of England made an agreement with "Senana wife of Griffin son of Llewellyn…whom David his brother keeps in prison with Owen his son" for payment of a ransom for their release, agreeing to give "David and Rothery her sons as hostages" to the king, dated 12 Aug 1241.
He married Elizabeth de Ferrieres, the widow of William Marshal, in 1277.
He married Elizabeth Ferrers, widow of William Marshall. 
She was the daughter of William Ferrers Earl of Derby & his second wife Margaret de Quincy of Winchester, who died in 1297. 
In 2223 Dafydd's father Gruffudd was entrusted by Llewelyn with a numerous army to oppose William Marshall, earl of Pembroke, who had returned from Ireland to South Wales, and had taken Aberteivi and Carmarthen from Llewelyn. A battle was fought by Carmarthen with doubtful result, but lack of provisions immediately afterwards obliged Gruffydd to retire to the north. 
This would presumably be an earlier William Marshall.
The Annals of Dunstable state that “David germanus Leulini principis Walliæ” married “filia comitis de Ferares” when recording that she was captured in 1283 with her husband and son. 
Dafydd had a mistress, Tangwystl ferch Owain "Fflam", with whom he had at least one child.
He also had numerous other mistresses prior to his marriage to Elizabeth and apparently had seven daughters from these liaisons.
The Continuator of Florence of Worcester records the rebellion of "Lewelinus princeps Walliæ…cum David germano suo" in  
1282 Prince of Wales
He succeeded his brother in 1282 as Dafydd III Prince of Wales.
The Annales Cambriæ record that "David" was captured and beheaded "in crastino Beati Michaelis…apud Slopesburiam" in 1283. 
Dafyyd was executed for high treason, hanged, drawn and quartered, on 3 Oct 1283 at High Cross, Shrewsbury, Shropshire, England.
By his wife Elizabeth de Ferrieres
Llywelyn ap Dafydd, b. Abt 1270, of, , Caernarvonshire, Wales, d. a prisoner in 1288 (Age ~ 18 years). He died in 1288. 
Owain ap Dafydd, b. Abt 1270, of, , Caernarvonshire, Wales, d. Aft 1305 (Age ~ 36 years) 
Gwladus ferch Dafydd, b. Abt 1270, of, Is Aled commote, Denbighshire, Wales , d. 1336 (Age ~ 66 years) The Annales Cambriæ record that "David cum duobus filiis uxore et filiabus" were captured "circa festum Nativitatis Beati Johannis Baptistæ" in 1283. Nuns. 
By his mistress, Tangwystl ferch Owain "Fflam",
Dafydd "Gôch" ap Dafydd, lord of Penmachno; m1. Angharad [2nd] ferch Heilin; m2. Angharad ferch Tudur
By other mistresses
Dafydd had numerous other mistresses prior to his marriage to Elizabeth and apparently had seven daughters from these liaisons.
↑ 1.01.1 The solid date upon which estimates can be based is 12 August, 1241. On that date, Senena, wife of Gruffudd, signed an agreement with King Henry III arranging for the release and restoration of her husband Grufudd and son Owain, leaving her youngest sons Dafydd and Rhodri as hostages in Owain's place. Henry broke the agreement, keeping Gruffydd prisoner in the Tower of London, but with generous provisions which included permission for Senena to stay with him. Gruffudd ended his life in a failed escape attempt on 1 March, 1244. These facts permit the following conclusions and date estimates:
Senena was Gruffudd's wife to the end. Any other wife would have to precede Senena.
Senena was exemplary in defending her husband before the king, assuming roles few women were accustomed to assume. This suggests their relationship was good and if he had any mistresses they probably preceded the marriage.
Owain was Senena's oldest son. For one of his age, hostage status meant being a prisoner with his father in the Tower of London, so estimate his age as 18 in 1241, thus born in 1223.;
Since Owain was the oldest and first born son, assume the marriage was the year prior to his birth, 1222.
Girls married very young; assume she was 16 at her marriage in 1222, thus born in 1206. Boyer shows Senena's father Caradog born, say, 1200. This estimation would require Caradog to marry in 1205 at the age of 20, and be born in, say, 1185, rather than 1200.
Dafydd and Rhodri, the youngest sons offered as exchange hostages, would have been much younger, and destined to live in a noble household. Assume they were just old enough to comfortably leave home in 1241, aged 9 and 6, thus born in 1232 and 1235, respectively.
Men tended to be older at marriage. Assume Gruffudd was aged 24 in 1222; this would place his birth at 1198.
If Grufudd had an additional relationship, whether in a marriage or with a mistress, assume it occurred between Grufudd becoming 18 in 1216, and his marriage to Senena in 1222.
Some sources refer to Gruffudd's additional marriage to Rhanultt ferch Rheinullt. Others refer to her as a mistress. Either way, the relationship and the children born of it would have occurred between 1216 and 1222.
Based on the above, Gruffudd's two oldest children, daughters Catrin and Gwladus, would have been born, say, 1217 and 1219. The remaining children, born to Senena, would have been born as follows: Owain, 1223; Llywelyn, 1225; Dafydd Felyn, 1227 and died early, Margred, 1229, Dafydd 1232, and Rhodri 1235. This date estimation is of course speculative and serves to place persons in the most appropriate time perspective, but hopefully the logic expressed above achieves the best possible date estimates.
↑Wikipedia: Gruffydd ap Llywelyn Fawr Follows Stephen, Leslie; Lee, Sidney, eds. (1890). "Gruffydd ab Llywelyn (d.1244)". Dictionary of National Biography. 23. London: Smith, Elder & Co. Accessed Feb 15, 2016 jhd
↑ Carl Boyer, 3rd. Medieval Welsh Ancestors of Certain Americans. By the Author: Santa Clarita, California, 2004. page 307
↑ Carl Boyer, 3rd. Medieval Welsh Ancestors of Certain Americans. Generally follows Bartrum. By the Author: Santa Clarita, California, 2004. Senena is the daughter of Caradog, #1 on page 57
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According to the sources for http://www.wikitree.com/wiki/Llywelyn-30 - the name of his father is not Gruffudd - it's Gruffydd - while the two names are interchangeable in many instances - this does not seem to be one of those cases.