Why does fool disappear at the end of act III?

There are a few explanations for this; one, the fool was actually Cordelia in disguise. If this was the case...... we see proof in Lear's comment,"My poor fool is hanged!"

Another belief is that the fool disappears when lear realizes that he himself is in fact the true fool. None-the-less, the Fool and Cordelia are never around at the same time, and both of them are gone when the King falls into a complete state of madness.