King Arthur and his Knights by Thomas Bulfinch

On arriving in Brittany Tristram found King Hoel engaged in a war with a rebellious vassal, and hard pressed by his enemy. His best knights had fallen in a late battle, and he knew not where to turn for assistance. Tristram volunteered his aid. It was accepted; and the army of Hoel, led by Tristram, and inspired by his example, gained a complete victory. The king, penetrated by the most lively sentiments of gratitude, and having informed himself of Tristram's birth, offered him his daughter in marriage. The princess was beautiful and accomplished, and bore the same name with the Queen of Cornwall; but this one is designated by the Romancers as Isoude of the White Hands, to distinguish her from Isoude the Fair.

How can we describe the conflict that agitated the heart of Tristram? He adored the first Isoude, but his love for her was hopeless, and not unaccompanied by remorse. Moreover, the sacred quest on which he had now entered demanded of him perfect purity of life. It seemed as if a happy destiny had provided for him in the charming princess Isoude of the White Hands the best security for all his good resolutions. This last reflection determined him. They were married, and passed some months in tranquil happiness at the court of King Hoel. The pleasure which Tristram felt in his wife's society increased day by day. An inward grace seemed to stir within him from the moment when he took the oath to go on the quest of the Holy Greal; it seemed even to triumph over the power of the magic love-potion.