prince harry arrives in australia next monday ahead of four-week stay .
he will fulfill a dream by training with the elite sas regiment in perth .
war hero and vc winner mark donaldson is an sas trainer in perth .
donaldson has written about how he saved the prince from the taliban .
donaldson and crack sas unit shot dead in 2009 a taliban warlord who boasted of killing prince harry .
prince will also go bush with indigenous norforce troops .
the royal said to be excited for ` challenging and hectic ' schedule .
the trip is the last of prince harry 's military career before he retires .