The princess featured in AoL is actually a different Zelda than the one seen in the NES prequel. AoL Zelda's story is told in the manual as "The Legend of Zelda", or as the Zelda community calls it; "The Legend of Sleeping Zelda". As the latter title suggests, it takes place centuries before AoL and it involves a mysterious wizard who casts a "sleeping beauty curse" on Zelda because she would not reveal the location of the Trifoce of Courage which the dead King passed on to her.
Impa is the one who actually tells Link this legend because it is his destiny is to awaken this sleeping Zelda by obtaining the Triforce of Courage and reuniting it with the other two pieces.
