Llew Llaw Gyffes, the son of Arianrhod, and Gwydion, the brother of Arianrhod, went unto Math the son Mathonwy, and complained unto him most bitterly of Arianrhod. Gwydion showed him also how he had procured arms for the youth. "Well," said Math, "we will seek by charms and illusion, to form a wife for him out of flowers." So they took the blossoms of the oak, the broom, and the meadowsweet, and produced from them a maiden, the fairest and most graceful that man ever saw. They baptized her, and gave her the name of Blodeuwedd.

After she had become his bride, and they had feasted, said Gwydion, "It is not easy for a man to maintain himself without possessions." "Of a truth," said Math, "I will give the young man the best Cantrev to hold." "Lord," said he, "what Cantrev is that?" "The Cantrev of Dinodig," he answered. Now it is called at this day Eivionydd and Ardudwy. The place in the Cantrev where he dwelt was a palace in a spot called Mur y Castell, on the confines of Ardudwy. There dwelt he and reigned, and both he and his sway were beloved by all.

One day he went forth to Caer Dathyl, to visit Math the son of Mathonwy. On the day that he set out for Caer Dathyl, Blodeuwedd walked in the court. She heard the sound of a horn. After the sound of the horn, a tired stag went by, with dogs and huntsmen following it. After the dogs and the huntsmen there came a crowd of men on foot. "Send a youth," said she, " to ask who yonder host may be." So a youth went, and inquired whom they were. "Gronw Pebyr is this, the lord of Penllynn," said they. Thus the youth told her. Gronw Pebyr pursued the stag, and by the river Cynvael he overtook the stag and killed it. With flaying the stag and baiting his dogs, he was there until the night began to close in upon him. As the day departed and the night drew near, he came to the gate of the Court. "Verily," said Blodeuwedd, "the Chieftain will speak ill of us if we let him at this hour depart to another land without inviting him in." "Yes, truly, lady," said they, "it will be most fitting to invite him." Then went messengers to meet him and bid him in. He accepted her bidding gladly, and came to the Court, and Blodeuwedd went to meet him and greeted him, and bade him welcome. "Lady," said he, "Heaven repay thee thy kindness." When they had disaccoutred themselves, they went to sit down. Blodeuwedd looked upon him, and from the moment that she looked on him she became filled with his love. He gazed on her, and the same thought came unto him as unto her, so that he could not conceal from her that he loved her, but he declared unto her that he did so. Thereupon she was very joyful. All their discourse that night was concerning the affection and love that they felt one for the other, and which in no longer space than one evening had arisen. That evening passed they in each other's company. The next day he sought to depart. But she said, "I pray thee go not from me to-day." That night he tarried also. That night they consulted by what means they might always be together. "There is none other counsel," said he, "but that thou strive to learn from Llew Llaw Gyffes in what manner he will meet his death. This must thou do under the semblance of solicitude concerning him." The next day Gronw sought to depart. "Verily," said she, "I will counsel thee not to go from me to-day." "At thy instance will I not go," said he, "albeit, I must say, there is danger that the chief who owns the palace may return home." "To-morrow," answered she, "will I indeed permit thee to go forth." The next day he sought to go, and she hindered him not. "Be mindful," said Gronw, "of what I have said unto thee, and converse with him fully, that under the guise of the dalliance of love find out by what means he may come to his death." That night Llew Llaw Gyffes returned to his home. The day they spent in discourse, and minstrelsy, and feasting. At night they went to rest, and he spoke to Blodeuwedd once, and he spoke to her a second time. But, for all this, he could not get from her one word. "What aileth thee," said he, " art thou well?" "I was thinking," said she, "of that which thou didst never think of concerning me; for I was sorrowful as to thy death, lest thou shouldst go sooner than I." "Heaven reward thy care for me," said he, "but until Heaven take me I shall not easily be slain." "For the sake of Heaven, and for mine, show me how thou mightest be slain. My memory in guarding is better than thine." "I will tell thee gladly," said he. "Not easily can I be slain, except by a wound. And the spear wherewith I am struck must be a year in the forming. Nothing must be done towards it except during the sacrifice on Sundays." "Is this certain?" asked she. "It is in truth," he answered. “I cannot be slain within a house, or without I cannot be slain on horseback nor on foot." "Verily," said she, "in what manner then canst thou be slain?" "I will tell thee," said he. "By making a bath for me by the side of a river, and by putting a roof over the cauldron, and thatching it well and tightly, and bringing a buck, and putting it beside the cauldron. Then if I place one foot on the buck's back, and the other on the edge of the cauldron, whosoever strikes me thus will cause my death." "Well," said she, "I thank Heaven that it will be easy to avoid this." No sooner had she held this discourse than she sent to Gronw Pebyr. Gronw toiled at making the spear, and in a twelvemonth it was ready. That very day he caused her to be informed thereof. "Lord," said Blodeuwedd unto Llew, "I have been thinking how it is possible that what thou didst tell me formerly can be true; wilt thou show me in what manner thou couldst stand at once upon the edge of a cauldron and upon a buck, if I prepare the bath for thee?" "I will show thee," said he. Then she sent unto Gronw, and bade him be in ambush on the hill that is now called Bryn Kyvergyr, on the bank of the river Cynvael. She caused also to be collected all the goats that were in the Cantrev, and had them brought to the other side of the river, opposite Bryn Kyvergyr. The next day she spoke thus. "Lord," said she, "I have caused the roof and the bath to be prepared, and lo! They are ready." "Well," said Llew, "we will go gladly to look at them." The day after they came and looked at the bath. "Wilt thou go into the bath, lord?" said she. "Willingly will I go in," he answered. So into the bath he went, and he anointed himself. "Lord," said she, "behold the animals which thou didst speak of as being called bucks." "Well," said he, "cause one of them to be caught and brought here." The buck was brought. Then Llew rose out of the bath, and put on his trousers, and he placed one foot on the edge of the bath and the other on the buck's back. Thereupon Gronw rose up from the hill that is called Bryn Cyvergyr, and he rested on one knee, and flung the poisoned dart and struck him on the side, so that the shaft started out, but the head of the dart remained in. Then he flew up in the form of an eagle and gave a fearful scream. And thenceforth was he no more seen. As soon as he departed Gronw and Blodeuwedd went together unto the palace that night. The next day Gronw arose and took possession of Ardudwy. After he had overcome the land, he ruled over it, so that Ardudwy and Penllyn were both under his sway. These tidings reached Math, the son of Mathonwy. Heaviness and grief came upon Math, and much more upon Gwydion than upon him. "Lord," said Gwydion, "I shall never rest until I have tidings of my nephew." "Verily," said Math, "may Heaven be thy strength." Gwydion set forth and began to go forward. He went through Gwynedd and Powys to the confines. When he had done so, he went into Arvon, and came to the house of a vassal, in Maenawr Penardd. He alighted at the house, and stayed there that night. The man of the house and his household came in, and last of all came the swineherd. Said the man of the house to the swineherd, "Well, youth, hath thy sow come in to-night?" She hath," said he, "and is this instant returned to the pigs." "Where doth this sow go to?" said Gwydion. "Every day, when the sty is opened, she goeth forth and none can catch sight of her, neither is it known whither she goeth more than if she sank into the earth." "Wilt thou grant unto me," said Gwydion, "not to open the sty until I am beside the sty with thee." "This will I do, right gladly," he answered. That night they went to rest; and as soon as the swineherd saw the light of day, he awoke Gwydion. Gwydion arose, dressed himself, and went with the swineherd, and stood beside the sty. Then the swineherd opened the sty. As soon as he opened it, she leaped forth, and set off with great speed. Gwydion followed her, and she went against the course of a river, and made for a brook, which is now called Nant y Llew. There she halted and began feeding. Gwydion came under the tree, and looked what it might be that the sow was feeding on. He saw that she was eating putrid flesh and vermin. Then looked he up to the top of the tree, and as he looked he beheld on the top of the tree an eagle, and when the eagle shook itself, there fell vermin and putrid flesh from off it, and these the sow devoured. It seemed to him that the eagle was Llew. He sang an Englyn: "Oak that grows between the two banks; Darkened is the sky and hill! Shall I not tell him by his wounds, That this is Llew?" Upon this the eagle came down until he reached the center of the tree. Gwydion sang another Englyn: "Oak that grows in upland ground, Is it not wetted by therein? Has it not been drenched By nine score tempests? It bears in its branches Llew Llaw Gyffes!" Then the eagle came down until he was on the lowest branch of the tree, and thereupon this Englyn did Gwydion sing: "Oak that grows beneath the steep; Stately and majestic is its aspect! Shall I not speak it? That Llew will come to my lap?" The eagle came down upon Gwydion's knee, and Gwydion struck him with his magic wand, so that he returned to his own form. No one ever saw a more piteous sight, for he was nothing but skin and bone. Then he went unto Caer Dathyl, and there were brought unto him good physicians that were in Gwynedd, and before the end of the year he was quite healed. "Lord," said he unto Math the son of Mathonwy, "it is fall time now that I have retribution of him by whom I have suffered all this woe." "Truly," said Math, "he will never be able to maintain himself in the possession of that which is thy right." "Well," said Llew, "the sooner I have my right, the better shall I be pleased." Then they called together the whole of Gwynedd, and set forth to Ardudwy. Gwydion went on before and proceeded to Mur y Castell. When Blodeuwedd heard that he was coming, she took her maidens with her, and fled to the mountain. They passed through the river Cynvael, and went towards a court that there was upon the mountain. Through fear they could not proceed except with their faces looking backwards, so that unawares they fell into the lake. They were all drowned except Blodeuwedd herself, and Gwydion overtook her. He said unto her, "I will not slay thee, but I will do unto thee worse than that. For I will turn thee into a bird; and because of the shame thou hast done unto Llew Llaw Gyffes, thou shalt never show thy face in the light of day henceforth; and that through fear of all the other birds. For it shall be their nature to attack thee, and to chase thee from wheresoever they may find thee. Thou shalt not lose thy name, but shalt be always called Blodeuwedd." Even today the word "Blodeuwedd" means owl in the Welsh language. Then Gronw Pebyr withdrew unto Penllyn, and he dispatched thence an embassy. The messengers he sent asked Llew Llaw Gyffes if he would take land, or domain, or gold, or silver for the injury he had received. "I will not, by my confession to Heaven," said he. "Behold this is the least that I will accept from him; that he come to the spot where I was when he wounded me with the dart, and that I stand where he did, and that with a dart I take my aim at him. This is the very least that I will accept."

This was told unto Gronw Pebyr. "Verily," said he, "is it needful for me to do thus? My faithful warriors, and my household, and my foster-brothers, is there not one among you who will stand the blow in my stead?" "There is not," answered they. Because of their refusal to suffer one stroke for their lord, they are called the third disloyal tribe even unto this day.

"Well," said he, "I will meet it." Then they two went forth to the banks of the river Cynvael and Gronw stood in the place where Llew Llaw Gyffes was when he struck him, and Llew in the place where Gronw was. Then said Gronw Pebyr unto Llew, "Since it was through the wiles of a woman that I did unto thee as I have done, I adjure thee by Heaven to let me place between me and the blow, the slab thou seest yonder on the river's bank." "Verily," said Llew, "I will not refuse thee this." "Ah," said he, "may Heaven reward thee." So Gronw took the slab and placed it between him and the blow.

Then Llew flung the dart at him, and it pierced the slab and went through Gronw likewise, so that it pierced through his back. Thus was Gronw Pebyr slain.

There is still the slab on the bank of the river Cynvael, in Ardudwy, having the hole through it. Therefore is it even now called Llech Gronw.

A second time did Llew Llaw Gyffes take possession of the land, and prosperously did he govern it. And as the story relates, he was lord after this over Gwynedd.