but that’s another story
From Longman Dictionary of Contemporary Englishbut that’s another storybut that’s another storyMENTIONused when you have mentioned something that you are not going to talk about on this occasion → storyExamples from the Corpusbut that’s another story• I did not get home till 6:00 am on sunday after the spurs game!!! but that's another story.• You could, of course, buy one of the super Chunky machines - but that's another story!• There's room for even more, but that's another story.• It also causes lucrative publicity and a scapegoat, but that's another story.• Like Birdie Walker, I survived, but that's another story.