What is sir Lucas's advice to Arthur? What does Arthur do? (Short story The Day of Destiny)

In the short story "The Day of Destiny" from Morte D'Arthur by Sir Thomas Malory, Sir Lucas advises King Arthur not to fight in the upcoming battle.

He also reminds him of the dream King Arthur had, in which Sir Gawain warned him about the outcome. He will die if he proceeds with his plan to fight Sir Modred.

When King Arthur and Sir Modred meet, they end up killing each other.