King Lear Act 3, Scene 3
Gloucester and Edmund appear on stage. Gloucester tells his bastard son that he doesn't like how Cornwall and Regan have suddenly assumed authority in his home. Edmund, lying, quickly agrees with his father that their behavior is "savage and unnatural." But we know Edmund is lying because he himself wants to overturn what is "natural."
Gloucester makes the quick mistake of telling Edmund that he's received a letter from French invaders saying they are planting their forces in England. Old Gloucester plans to disobey Cornwall's orders and go to the king with whatever comfort he can provide. He asks his son to lie for him by saying that Gloucester has gone to sleep early for the evening due to an illness. Once Gloucester leaves, Edmund reveals that he will betray this confidence to advance his cause.