How does Merlin arrange for king uther to lie with igraine?

Merlin arranges for King Uther to lie with Igraine by using a magical deception. He transforms Uther's appearance to resemble Igraine's husband, Duke Gorlois, enabling Uther to enter their castle without raising suspicion. This plan is orchestrated to ensure that Uther can father a child, Arthur, who is destined for greatness. Ultimately, Merlin's intervention is pivotal in changing the course of destiny for both Uther and England.