Sir Valentyne was a knight of Lombardy, the northern Italian realm famed for its mercenaries and its wealth, a man of such extraordinary stature that poets measured him at fifteen feet from sole to crown. He was the lord of Atalye, a territory within his northern domain, and he commanded the loyalty of many Lombard knights who rode at his side. His fame as a warrior had spread through the courts of Europe, but it was the sudden renown of Sir Launfal, the impoverished steward of King Arthur's court who had returned from fairyland with magical gifts, that roused Valentyne to envy. The English knight had won a tournament at Carlisle, the northern city on the border of Arthur's realm, and his victory there made his name a byword for chivalric excellence. Valentyne could not endure that a mere steward, however fairy-blessed, should outshine the giants of Lombardy. He sent a messenger to Arthur's court bearing a challenge written in the language of courtly love and martial pride, a summons that would force Launfal to leave England and fight on foreign ground.

The challenge that Valentyne issued was worded with cunning precision. He commanded his herald to tell Launfal that he must come to Lombardy to joust, and that the honour of his beloved lady was the stake. The message ran thus: say to him, for love of his leman, if she be any gentlewoman, courteous, free, or kind, that he come to juste with me to keep his harness from the rust, or else his manhood be shamed. The phrase was a trap. By invoking Launfal's lady, Valentyne made the duel a test of Tryamour's nobility as well as Launfal's courage, for if the English knight refused, he would be declaring that his fairy mistress was unworthy of such a contest. The mention of rust-free armour mocked the very idea of knightly idleness, suggesting that a true knight must fight constantly or his gear would decay. And the threat to Launfal's manhood made the challenge personal and absolute. Launfal had no choice but to accept.

The combat took place on the tournament fields of Lombardy, with the lords of Atalye looking on. Valentyne was so vast that his horse must have been a destrier of unnatural proportions, his lance a beam of timber, his armour thick enough to stop a normal blade. When the two knights charged, Valentyne's strength was overwhelming. He struck Launfal with such force that the English knight's helmet flew from his head and his shield shattered against his arm. Without the fairy gifts he had received from Lady Tryamour, Launfal would have been unhorsed and slaughtered in that first pass. But Gyfre, the invisible dwarf servant who attended him, leaped onto Launfal's steed and pressed the fallen helmet back onto his master's head, then restored his shield to his arm, all without Valentyne or the Lombard spectators seeing a hand move. The giant struck again and again, and each time Gyfre repaired the damage, turning a mortal contest into a grotesque pantomime in which Launfal could not truly lose yet could not win by his own strength alone.

The end came when Launfal, kept alive by invisible hands, found his opening and drove his sword through some gap in the giant's armour. Valentyne fell, fifteen feet of Lombard pride crashing to the Italian dust. But the death of the champion did not end the battle. The Lombard knights who had ridden with Valentyne attacked Launfal in a body, seeking to avenge their lord, and Launfal was forced to cut his way through them all, slaying many before he could escape the field. The massacre that followed the single combat was neither chivalric nor glorious; it was the violence of survival, the fairy-aided knight hacking through mortal men who could not see the dwarf that saved him. When the news reached King Arthur at Carlisle, it was told as a tale of Launfal's nobleness, but the poem hints at something more complicated, a victory won by magic rather than manhood, by the invisible servant of a fairy queen rather than the arm of an English knight.

Valentyne's name carried its own irony. In the medieval world, the name Valentine was already associated with love, with the feast of lovers, and with the tender exchange of tokens between sweethearts. To give that name to a fifteen-foot giant whose only role is to threaten, batter, and ultimately die in a foreign tournament was to create a deliberate contrast, a figure who embodies masculine potency in its most terrifying and least romantic form. Some scholars have seen in him a symbolic challenger, the phallic adversary who tests whether Launfal's fairy love has truly made him a man or merely a puppet of supernatural power. His death proves that Launfal can survive such a test, but it also proves that he cannot survive it alone. The giant of Lombardy dies so that the romance can continue, his body left on Italian soil while Launfal rides back to England and the disaster of Guinevere's slander.