Complex sentence: In the final episode during the end credits when Professor Dementor asks him about this, and he begins to tell the story as the screen fades out, revealing only that the incident happened on a Tuesday.
Split into simpler sentences: In the final episode during the end credits, Professor Dementor asks him about this, and he begins to tell the story as the screen fades out. However, his explanation is cut short as the episode (and the series) ends, revealing only that the incident happened on a Tuesday.