Thanks to the combined magic of Princess Cadence and Shining Armour, Queen Chrysalis and her entire changeling horde were banished from Canterlot. While flying, Chrysalis was flying by one of her changeling soldiers.
Changeling: Well, this plan of yours was a complete disaster.
Chrysalis (annoyed): Shut up, no.109.
Soon, the entire changeling army was gone. All of Canterlot was spared the worst attack in history. Meanwhile, inside the wedding hall, the bride and groom, Shining Armour and Cadence along with Princess Celestia, and the Mane 6 celebrated their victory. But, it was a hollow victory because Twilight was not happy because the invasion was caused by the negligence of her brother, her friends and mentor Celestia.
Shining Armour (sighs): It's over. It's all over.
Twilight: Yea. It is.
As everyone celebrated, Twilight began walking to the doors unnoticed. It was obvious, she didn't want to stick around. But, Applejack notices and runs to catch up to her.
Applejack: Sugarcube, where are you going? Aren't you going to stick around?
Twilight (upset): No, I don't want to stick around.
Rarity (confused): Why not darling? With the changeling army gone, now's the right time to get the wedding back on track.
Twilight turns around with an angry look on her face. Everyone began to show looks of confusion on their faces. They all tried to figure out what Twilight was angry about. Twilight began seething with anger at her friends, brother and mentor for not figuring out what Twilight was upset about.
Twilight (angry): Oh come on, think back! The wedding rehearsal! I tried to warn you guys about the Cadence imposter, but no, you guys were too busy with the wedding to even think about the coming invasion!
Everyone was in complete shock was what Twilight said. Cadence had a look of confusion trying to figure out what Twilight was talking about. Everyone knew that it was true. They hung their heads in shame except for an upset Rainbow Dash.
Rainbow Dash (angry): Oh, shut up, Twilight! You're acting like a bratty foal like you did at the rehearsal and you should've been arrested instead of throwing you out of the wedding!
Hearing that, Twilight charged and tackles Rainbow Dash to the floor, leading to a massive brawl. The fight rolled around the entire hall and both ponies landed punches on each other. Applejack, Rarity, Pinkie Pie, Fluttershy, Spike, Shining Armour, Cadence, and Celestia watched in complete horror. Pinkie pie ran over to the two and attempted to stop the fight.
Pinkie pie: Twilight, stop! Rainbow dash is your friend!
Twilight Sparkle: No chance, Pinkie! Rainbow Crash is not my friend is not my friend anymore! None of you are!
The brawl continued for several minutes and rolled around the entire hall. Eventually, Shining Armour, and the others friends ran over and broke up the fight. Shining Armour held his sister back while Applejack, Rarity, and Pinkie Pie held Rainbow Dash back.
Twilight (angry): Grr! Put me down, Shining Armour! I'm not done with that big mouthed, backstabbing weasel!
Shining Armour: Not till you cool off, Twilight! Otherwise, you will leave no choice but to have you arrested!
Hearing what her own flesh and blood just said, Twilight head-butts him causing him to drop her. Then, using her magic, Twilight lifts her brother up and tosses him into her ex friends. Celestia runs over to Twilight, places her hoof on Twilight's shoulder and she attempts to reason with Twilight.
Celestia: Twilight, please I –
But, Twilight brushes Celestia's hoof away causing everybody to gasp in complete shock including Celestia herself. It was at that very moment Twilight had hit her boiling point.
Twilight (angry): So after all I did for you guys, you want to have me arrested! I'm done! I hereby quit as your student Celestia!
Shining Armour: But, Twiley, you can't just quit as Celestia's student! If I didn't know any better, you're being a selfish brat!
Upon hearing what her brother said, Twilight had lost it and punched her brother, knocking out one of his teeth in the process.
Twilight (angry): First, Shining Armour, don't call me Twiley anymore and second, my decision is final! And everything I ever learned about friendship didn't matter to them in the wedding rehearsal! Those five are the opposites of the elements of harmony and I'm done with them! If you all want to see too you're wedding, find some other sucker to do it, I'm out of here! Good-bye forever!
With that, Twilight began taking her leave. But, stops and looks back to see Spike with a sad look. She snorts at him, uses her magic to open the door, exits and slams them behind her.
Rainbow Dash (angry): Fine! Go ahead! We don't need a joke like you! In fact, you should've been banished!
It was at that moment, Shining Armour's wedding came crashing down and it was all because of his actions at the wedding rehearsal along with the mane 5 and Celestia.