J. Beverley Smith, in his exhaustive history of Llywelyn ap Gruffydd, lists primary sources for his research in the back of his book Llywelyn ap Gruffydd: The Prince of Wales, (Cardiff: University of Wales Press, 1998).

In perusing the documents, it becomes clear that while the thirteenth century was no longer officially the ‘dark ages’, there is very little documentation for an enormous amount of what happened in Wales during Llywelyn’s reign. On one hand, we have the cryptic Chronicle of the Princes (from which I quoted a few days ago), but no other record, official or otherwise, of the events leading up to Llywelyn’s death.

In addition, we don’t know:

1) When Llywelyn ap Gruffydd was born

2) If Senana was definitively his mother, though there is reference to him as the ‘uterine brother’ of Owain and Dafydd.

3)  Where he was when his family exchanged inprisonment in Criccieth Castle for the Tower of London.

4)  What his relationship was with his Uncle Dafydd.

5)  What happened in the belfry at Bangor and who betrayed him in 1282.

This is in large part, I suspect, because the English did everything they could do destroy all knowledge and records of the Welsh royal house, but it seems astonishing that no historican/churchman/author at the time, thought the events leading up to December 11th were important to record, immediately after the event. It may be that the English didn’t realize exactly how momentous his death really was, or Edward didn’t want to encourage any discussion of him at all.

What we do have is letters back and forth between Edward, Llywelyn, and the Archbishop of Canterbury. Some of these translations can be found here:
http://garthcelyn.com/letters_14.html

As well as: http://www.maryjones.us/ctexts/index_welsh.html

As with the conquests of his grandfather, Llywelyn Fawr (posted here:  https://sarahwoodbury.com/?p=2297), Llywelyn is mentioned extensively in The Chronicle of the Princes, particularly again, the Ystrad Fflur version.  Some samples:

1246 In this year the shield of Wales, Dafydd ap Llywelyn, died in his court at Aber; and his body was buried at Aberconwy with the body of his father. And since he had no heir of his body, there ruled after him the sons of Gruffudd, Owain Goch and Llywelyn. And those by counsel of the wise men of the land, divided the territory into two halves between them.

1260 In this year Llywelyn ap Gruffudd went to the land of Builth; and he took that land from Roger de Mortimer. And Owain ap Maredudd of Elfael came to Llywelyn’s peace.

1267 In this year Llywelyn ap Gruffudd made a pact with the earl of Clare. And after that the earl gathered a mighty host and made for the city of London; and forthwith through the deceit and treachery of the burgesses he took the city. And king Henry and Edward, his son, forced the earl to submit.  And peace and concord were arranged between Henry, king of England, and the Lord Llywelyn, prince of Wales, with Ottobon, the Pope’s legate, as mediator between them, at Baldwin’s Castle. And for that peace and agreement he promised to the king thirty thousand marks of the king’s sterling. And the king granted that the prince should receive the homage of the barons of Wales, and that the barons should maintain themselves and their followers wholly under the prince, and that there should be princes of Wales from that time forth, and that they should be so named. And that was also ratified by the authority of the Pope.