What was the book C.S. Lewis wrote last?

This is a tough question for anyone who likes C S Lewis as much as I do.....

Let's separate his books into fiction and non-fiction.

For fiction, number 1 has to be The Lion, The Witch, and the Wardrobe. The second best fiction book IMHO is The Screwtape Letters. For non-fiction, Mere Christianity is first with The Problem Of Pain being second.

You might want to listen to my podcast on the essential C S Lewis reading list at

http://allaboutcslewis.com/