Hm...
When I find out about the hero, I will proceed to kill his mother (or her father. They never have both parents.)
During his quest to gain revenge on me, I will begin presenting him with no win scenarios. He either has to sacrifice something, or stand by and do nothing. I will intersperse these with occasions where through lots of hard work, effort and out of the box thinking, he CAN save everyone without compromising his morals. These will be exceedingly rare, and that will make them all the more precious.
I will also spread rumors about how the evil overlord hasn't been seen since his battle with the Sage of Light, which took place X years ago, which just so happens to be how old the Hero is. Additional investigation into this will revealed damaged/destroyed statues that bear an uncanny resemblance to their parent, and most statues of the Villain will look like the Hero, aged up a couple of decades.
I will instruct my Commanders to act somewhat confused when they first see the Hero, before enaging him in battle, declaring it a trick. If they are killed their last words will be "Sir...why?" or somethign similar. If I have an attractive and sexually compatible commander, they will kiss the Hero and say, "I... always...loved you..."
I will manipulate him into venturing into other lands, which will inevitably be worse than my own, either due to cruel leaders, famine, plague, war or some other problem. Any nearby "good" kingdoms will have their leaders assassinated and replaced with doppelgangers, and probably practcing evil religion or human sacrifice.
All of these combined will make him start to doubt whether I am truly evil, or simply making the best of a bad situation. The inability to talk to his mother and the similarities to the Sage of Light, plus his own uncanny resemblance to statues of the Villain will make him question his own existence, if it's possible that he might be...
And then, when he reaches my castle, I will answer the door with a joyous "Master! You've finally returned! It's so good to see you again!"
Assuming I can manage to convince him that he is actually the villain, I can see only a few options:
1: He assumes the role of villain. I get to retire, or at least wait until the next upstart topples him.
2: He commits suicide.
3: He destroys my evil empire (I can make a new one,) but is haunted by the fact that he killed the people closest to him (My commanders).
4: 1 or 3, but his companions abandon him in disgust for who he really is. One or two might remain, but the stain of the "truth"
I could probably churn out a couple more scenarios, but it's late. I'll come back to this later. Maybe.