This maiden, as good and gentle as she was beautiful, soon fell in love with the handsome knight, and hearing him sing a passionate lay in honor of Iseult, she fancied that her affections were returned, and that it was intended for her ear.
"I know her by her mildness rare, Her snow-white hands, her golden hair; I know her by her rich silk dress, And her fragile loveliness,-- The sweetest Christian soul alive, Iseult of Brittany." MATTHEW ARNOLD, _Tristram and Iseult_.
The brother of this fair Iseult saw her love for Tristan, and offered him her hand, which he accepted more out of gratitude than love, and in the hope that he might at last overcome the effects of the fatal draught.

But, in spite of all his good resolutions, he could not forget Iseult of Cornwall, and treated his wife with such polite coolness that her brother's suspicions were finally roused.
Tristan, having conquered a neighboring giant and magician by the name of Beliagog, had granted him his life only upon condition that he would build a marvelous palace in the forest, and adorn it with paintings and sculptures, true to life, and representing all the different stages of his passion for Iseult of Cornwall.

When his brother-in-law, therefore, asked why he seemed to find no pleasure in the society of his young wife, Tristan led him to the palace, showed him the works of art, and told him all.
Ganhardin, the brother-in-law, must evidently have considered the excuse a good one, for he not only forgave Tristan, but implored him to take him to Cornwall, for he had fallen in love with the picture of Brangwaine, and hoped to win her for wife.

On the way thither the young knights met with sundry adventures, delivered Arthur from the power of the Lady of the Lake, and carried off Iseult, whom the cowardly Mark was ill treating, to Lancelot's castle of Joyeuse Garde.

There she became acquainted with Guinevere, and remained with her until Arthur brought about a general reconciliation.
Then Tristan once more returned to Brittany, resumed his wonted knightly existence, and fought until he was wounded so sorely that Iseult of Brittany could not cure him.