(The prompt: Write an AU story based on an episode of the show, in which a character’s faulty assumptions or decisions about a situation turn out to have been correct all along.)
She was stunning. Absolutely beautiful. Prince Blueblood watched the white unicorn mare carefully, though he was adept enough at seeming as though he wasn't. She was plainly trying to act far above her station, a peasant in princess clothing. She was also quite plainly posing for him. Still, she was quite attractive, and there was something there, something under the surface, that left him quite unable to completely ignore her.
He trotted toward her as soon as she looked away, and slowed to a quiet walk as he drew near. She sniffed at one of the roses, with a gentle smile on her lips, and he felt his heart move just seeing such an innocent gesture. So many of the mares he knew, the uptight nobles and the social climbing peasantry of Canterlot, would never have even noticed the brilliant plantings in the castle courtyard. He closed his eyes, adopting his most regal tone. "Well hello. I am Prince Blueblood."
The mare turned aside with what appeared to be genuine bashfulness. "I am... Rarity." She turned back toward him, and daintily lifted a hoof. Her voice changed just slightly, and Blueblood could almost picture her putting a mask on. She was faking being a noble, though she was doing such a poor job of it that it took effort not to correct her. "Oh my, what a lovely rose!"
However, he could show her how the nobility truly was, eventually. For now, he couldn't bring himself to miss this chance. "You mean, this rose?" He leaned in and picked it, and then stepped forward, sliding it carefully between two tresses in her mane, exactly where it wouldn't detract from her absolutely exquisite styling. "It isn't half as beautiful as the mare who wears it."
Prince Blueblood couldn't help but smile at the gentle, heartfelt blush that spread over the unicorn's cheeks. She wasn't one of the Canterlot elite, and her every motion, so genuine and true, proved exactly that. She had obviously been seeking him, and a few minutes careful conversation revealed as much. Still, despite the artifice around their meeting, Prince Blueblood had a real interest in this mare, and for the first time in years, poured himself into making another pony happy.
The courtship was not a long one. In fact, despite a few hiccups along the way, including one incident of shielding the mare with his body in defense against airborne baked goods, he found himself completely enamored as the night went on. The smell of apple frosting was annoying, yes, but the Gala continued even after Rarity's maddened yellow pegasus friend drove dozens of animals into the ballroom.
Her friends left, eventually, and Rarity and Blueblood shared a lovely waltz, the last of the evening. Somehow, Prince Blueblood knew that if he let this mare go back to Ponyville without telling her what she had come to mean to him, he would lose her.
He smiled, and though he had no ring, he asked. Rarity accepted, and Prince Blueblood's life would never be the same.
--
Prince Blueblood soon discovered just how amazing this mare was. Their wedding was perfect in nearly every way, despite the unintentional interruptions her friends tended to cause. She was endlessly generous and kind, and as skilled a designer as any pony in Canterlot. She missed Ponyville, and her friends missed her. Still, his influence managed to fast track Rainbow Dash into the Wonderbolts, and his bits paid for many trips for her friends and Rarity herself to and from Ponyville, for visits and frivolity.
When Discord returned, Prince Blueblood spent two days in terror for his wife as she faced an ancient, unknown evil. She returned to him, with scuffed hooves from digging, and shame in her eyes, but she returned victorious. He stood by her as she braved the world of the nobility, and assisted her in handling the lies and backhanded compliments that came through the plastic smiles of each and every noble pony he knew.
He was alongside her, helping with each difficult movement and each new stress during the wedding of Princess Cadance and Captain Shining Armor. He imposed himself between the Queen of the Changelings and his beautiful wife when the monster revealed herself. He supported her and her friends in their desperate struggle, and stood in awe with them as the love of the two engaged ponies defeated the hordes.
Prince Blueblood helped her to draft a suitably apologetic letter expressing regret that she couldn't assist with the troubles of the Crystal Empire. She was quite heavily with foal, and so much activity was simply something she could not safely handle. Her friends all understood. He stood with Rarity as they watched the others leave for the Empire. He stood by her as she listened to the story the ponies that made it back told her, and he held her close as she cried at the loss of Spike, so far from home.
The letters came less and less frequently, as time went on. Her friends had their own lives, in Ponyville, and caring for the young twins took nearly all of Rarity's time, as well as nearly all of Blueblood's. She was happy though, living in the lap of luxury, and they were very much in love. They spent their days tending to the foals, and their nights at home, cuddling warmly and simply enjoying one another's company as they had since their first meeting.
Then the Princesses disappeared, and the vines took Ponyville. The Everfree Forest was expanding. Nopony knew what was happening, and Princess Cadance, the only alicorn Princess that anypony could find, returned to Equestria too late to make a difference. Twilight Sparkle and her friends fought valiantly in Ponyville, but were unable to turn the tide.
Blueblood and Rarity stood with them, as the vines lashed and tore at Shining Armor's shield around Canterlot, even as his little sister bolstered it as best she could. Canterlot was the last holdout in Equestria, but it was no use. It was only a matter of time before the shield would fall. Prince Blueblood prayed, he cried out to the heavens and to the Princesses presumed dead to help him find some way to save his wife.
The world stopped as his prayer was answered. The only creature moving was Discord, the spirit of chaos and disharmony. He dragged his claw along Rarity's coat, and then turned to Prince Blueblood. The invasion was more than he had ever planned, and certainly more than he wanted now that he was friends with Fluttershy. By now, however, it was too late to stop. Discord smiled as he explained how he'd planted the seeds of this destruction, ages ago, and laughed as Blueblood attempted to stomp him into paste.
There was only one way to fix it. Discord could see the threads of destiny, he explained, and could spot exactly where they'd snagged. One small change, and everything would be again woven in such a way as to fix this.
--
She was stunning. Absolutely beautiful. Prince Blueblood fought back tears as he watched the unicorn mare carefully. She was acting above her station, a habit she'd never quite been able to drop. She was posing for him, and he longed desperately to sweep her off her hooves and give her the world. There was something though, something he had to do, that he was unable to completely ignore.
He walked slowly toward her, dragging his hooves in a very unroyal way. She blithely sniffed at the flowers, her beautiful lashes and that delicate smile on her lips quite nearly breaking his resolve. She was so beautiful, and so pure. He closed his eyes as he approached, and spoke in a slightly haughty, regal tone. "Well hello. I am Prince Blueblood."
She turned aside with her adorable embarrassment, and spoke carefully, in the tone he recognized now as nervousness hidden behind a false noble accent. "I am... Rarity. Oh my, what a lovely rose!"
Prince Blueblood looked down at the beautiful mare, and the stunning rose. It was such an easy action, to sweep her off her hooves again. This mare, this beautiful, perfect unicorn that he loved so dearly. His wife, the mother of his foals. But she wasn't now, and, well... She was more important than he was. She could be happy without him. "You mean, this rose?"
Blueblood picked the rose with his teeth, hesitated a half second more, and then clipped the stem short, and stuffed it into his lapel. He fought back the revulsion he felt for himself, and avoided looking into Rarity's disappointed eyes as best he could, as he haughtily spoke the sentence that changed history. "Thank you. It goes with my eyes."