Okay, if you insist:
You guys remember how in the two-part season 2 finale episode, A Canterlot Wedding, Twilight got dismissed by her friends, Shining Armor and Princess Celestia for blindly accusing Cadence of being evil because of her nasty attitude towards her friends and seeing her cast a weird spell on Shining Armor? And then later, it turned out Cadence was actually Chrysalis, Queen of the Changlings in disguise and after the Mane 6 were captured by her, only Applejack was shown apologizing to Twilight for not believing her?
Well, one person by the name of Darth Link 22 believed that it wasn't enough to just have Applejack apologize for everypony shunning Twilight and decided to write Post Nuptials, depicting how guilty the other Mane 6 characters, Spike, Shining Armor and Princess Celestia feel for how they let her down, as well as having Twilight realize her own mistake of just accusing the fake Cadence without solid evidence or going to talk to the Princess about it.
The chapters of the story take place between scenes of the ending of Part 2.