From Geoffrey of Monmouth’s History of the Kings of Britain (c.1139), Book 2 chs. 12-15

Landing at last, his mind filled with these reflections and others of a like kind, [Lear] came to Karitia, where his daughter lived, and waiting without the city, sent a messenger to tell her into what indigence he had fallen, and to beseech his daughter's compassion inasmuch as he had neither food nor clothing. On hearing the tidings, Cordelia was much moved and wept bitterly. When she made inquiry how many armed men he had with him, the messengers told her that he had none save a single knight, who was waiting with him without the city. She commanded also that he should have a retinue of forty knights well appointed and armed, and that then he should duly announce his arrival to Aganippus and herself. The messenger accordingly forthwith attended King Lear into another city, and hid him there in secret until that he had fully accomplished all that Cordelia had borne him on hand to do.

As soon therefore, as he was meetly arrayed in kingly apparel and invested with the ensigns of royalty, and a train of retainers, he sent word unto Aganippus and his daughter that he had been driven out of the realm of Britain by his sons-in-law, and had come unto them in order that by their assistance he might be able to recover his kingdom. They accordingly, with the great counselors and nobles, came forth to receive him with all honour, and placed in his hands the power over the whole of Gaul until such time as they had restored him unto his former dignity.

In the meanwhile, Aganippus sent envoys throughout the whole of Gaul to summon every knight baring arms therein to spare no pains in coming to help him to recover the kingdom of Britain for his father-in-law, King Lear. When they had all made them ready, Lear led the assembled host together with Aganippus and his daughter into Britain, fought a battle with his sons-in-law, and won the victory, again bringing them all under his own dominion. In the third year thereafter he died, and Aganippus died also, and Cordelia, now mistress of the helm of state in Britain, buried her father in a certain underground chamber which she had bidden be made under the river Soar at Leicester. This underground chamber was founded in honour of the two-faced Janus, and there, when the yearly celebration of the day came round, did all the workmen of the city set hand unto such work as they were about to be busied upon throughout the year.

Now, when Cordelia had governed the kingdom in peace for five years, two sons of her sisters began to harass her, Margan, to wit, and Cunedag, that had been born unto the Dukes Maglaunus and Henvin, both of them youths of notable likelihood and prowess, Margan being son of Maglaunus and Cunedag of Henvin. These, after the deaths of their fathers, had succeeded them in their dukedoms, and now took it in high dudgeon that Britain should be subject to the rule of a woman. They therefore assembled their hosts and rebelled against the Queen, nor were they minded to put an end to their outrages until after laying waste a number of provinces, they had defeated her in several battles, and had at last taken her and put her in prison, wherein, overwhelmed with grief for the loss of her kingdom, she slew herself. Forthwith the youths divided the island between them, whereof that part which stretcheth from the Humber towards Caithness fell to Margan's share, and the other, on the other side of the river, that vergeth toward the West, was allotted to Cunedag.