Incoming the swarm of finale clips! This specific one can be found over at io9. They also have a new synopsis up, find that after the break.
In the two-part episode "A Canterlot Wedding," the kingdom is in a frenzy preparing for the wedding of Princess Celestia's niece, Princess Cadance, to Twilight Sparkle's brother, Shining Armor. However, Twilight Sparkle discovers a dark secret about the bride that could ruin her brother's "happily ever after."