isn't that the Oedipus paradox? where his father was told of his doom, that his son would end his life, marry his own mother, and bring doom upon the land etc.
the king did everything in his power, exercising his free will, to stop it from happening, but in the end it was his own "choices" that led to his doom at the hands of his son.
ergo, his destiny was predetermined, and while he believed he made every logical choice to avoid it, against all reason, his choices led to the occurance. so his free will was merely an illusion anyway.
one can't change the direction of their fate, if there is indeed such a thing.