Macbeth receives three prophecies fromt the witches in Act IV scene 1, and the conclusion of this excellent tragedy shows those prophecies coming to fruition and resulting in Macbeth's premature end. The three prophecies were that he should beware Macduff, he will not be slain by any man born of woman, and lastly that until Great Birnam Wood come to High Dunsinane hill, he will not be vanquished. These prophecies fill Macbeth with great hope, as he does not see how anybody can kill him.
However, in Act V, these prophecies are fulfilled. He finds out that Macduff is fighting against him, enraged at Macbeth's slaughter of his family. Great Birnam Wood does move against him, and lastly, as he discovers to his surprise, Macduff was not "born of woman":
Despair they charm;
And let the Angel, whom thou sill serv'd.
Tell thee, Mcduff was from his mother's womb
In this quote, Macduff reveals he was born by caesarean and therefore was not "of woman born" in the way meant by the witches. Macbeth thus realises that Macduff is the character who will seal his doom. The play ends with Macbeth being killed by Macduff in revenge for the slaughter of his family and Malcolm winning his rightful inheritance and becoming King of Scotland.