It's a long story

It's a long story.

something that you say when someone has asked you about something that happened and you do not want to explain it to them because it would take too long 'So why was Carlo knocking on your door at midnight?' 'It's a long story.'
See also: long, story
References in classic literature ?
Yes, I have been to Barsoom again, and--but it's a long story, too long to tell in the limited time I have before I must return.