The person whom the story belongs to is not telling the story, but someone else is telling it on his behalf. In that case, what's one concise word or phrase to replaced the bold part above?
This story is recounted by another person on behalf of the original person that experienced this story.
This phrases is added before the actual story is recounted, so this is pretty much a reminder to the audience that the person they see telling the story is not the real guy. The best I can get to is "This story is recounted by someone else on behalf of the true protagonist," but that still sounds off.