What is the meaning “这是后话”? Does it mean 'another story'?
This is the phrase that came to my mind first.
Is there any other corresponding English phrase?
The counterpart of “这是后话” in English should be " That is a story for another time." meaning some future events are related to the story, but not the focus of the current story arc. The author may or may not revisit it in later part of the story.