Answer:
In King Arthur's Knights, King Anguish send La Belle Isoude and Sir Tristram off with a heavy heart because He was afraid that Sir Tristram would steal La Belle Isoude away from King Mark on the journey.
Step-by-step explanation:
As La Belle Isoude and Sir Tristram had a relationship, King Anguish shows his concerns about what they were really going to do when they were sent on that journey, he was not sure if he was able to trust Sir Tristram in going according to the plan or if he was going to take his beloved one away, so the couple will never be found.