In a medium bowl, blend together condensed milk, lime juice and zest. Mix in egg yolks and whole egg. Pour mixture into crust, then cover and refrigerate for 1 hour.
Preheat oven to 350 degrees F (175 degrees C).
To Make Meringue: In a large glass or metal mixing bowl, beat egg whites until foamy. Gradually add sugar, continuing to beat until whites form stiff peaks. Spread meringue over pie, covering completely.
Bake in preheated oven for 15 minutes. Chill before serving.