Macedon is not Worthy of Thee
is what Philip said to his son Alexander, after his achievement with the horse Bucephalos, which he subdued to his will, though only eighteen years of age.
Edward III., after the battle of Crecy, in which the Black Prince behaved very valiantly, exclaimed, “My brave boy, on as you have begun, and you will be worthy of England's crown.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Macedon is not Worthy of Thee from Infoplease: