(Warnings: THE RED WEDDING!! DEATH, BLOOD. Slight AU)
Y/N smiled as his twin spoke the vows uniting him with Talisa for life. When the ceremony was complete, Y/N watched as Robb walked away with his new bride and he sighed. His identical twin was happier than Y/N had ever seen him and that was worth all the tears and frustration the war had caused. Still, Y/N couldn't shake the feeling that something bad was about to happen. Robb had to consummate his marriage though, so Y/N sought out his mother.
"Mother?" Y/N called from outside her tent, not wishing to walk in on her changing. Catelyn bid her son enter. "Y/N. What troubles you?" Y/N smiled. His mother was the only person who could tell the twins apart. Even Ned would mix the two up when he was alive. "I just have a bed feeling. Something terrible is going to happen to Robb." Catelyn's brows furrowed. "What, my child?" Y/N sighed. "I don't know. I cannot shake the feeling though." Catelyn could not offer her son any advice so, the young man went to his own tent.
Some time later, the feeling in Y/N's gut still wouldn't go away. Something was going to happen to his twin if he didn't stop it. The only problem was that Y/N didn't know what would happen. As they approached the Twins, the feeling grew and, when a wedding between his uncle and Roslin Frey was announced, Y/N knew exactly what to do. Now, he just had to convince Robb to go along with it.
"Robb, please listen. You cannot go. Something is going to happen to you. Let me go in your stead. They will not know the difference, except for Mother. I will simply say that Y/N has gone on ahead to try and recruit more men. They will believe it. Just...please Robb." Robb gazed at his brother in shock. Y/N was always the more sensitive of the two of them and Robb had learned to trust his twin's gut feelings. If he said something wasn't right, then something wasn't. "Alright, but know I will be watching." Y/N nodded and dressed in Robb's clothing for the wedding.
Y/N took Talisa's arm and lead her into the great hall of the Twins. As the two of them walked, Talisa whispered, "Where is Robb?" Y/N chuckled. "How did you know? No one has ever been able to tell the two of us apart except for Mother." Talisa smiled. "I have known your brother's touch for many moons now. Yours is different." Y/N nodded in understanding, but didn't have a chance to explain what was happening before the two of them were in their seats and the merriment began.
After a while, Walder Frey gave "Robb" the honor of announcing the bedding. As the newlyweds were carried from the room, the doors were closed and barred. Y/N stomach twisted, knowing that something was about to happen. He was right. All hell broke loose. Arrows were flying, swords were clashing and, before he could stop it, Y/N saw his brother's wife stabbed repeatedly in the stomach. In his distraction, he hardly noticed the arrows sinking into his flesh.
Y/N felt his eyes go wide as Roose Bolton approached him. Roose grabbed Y/N, wrapping one arm around him while the other held a knife. "The Lannisters send their regards," was all he said before plunging the knife into Y/N. The young man fell to the floor next to his goodsister, blood pouring from the wound. Y/N's eyes scanned the room, briefly landing on his mother before the light left them.
Catelyn's anguished cries drowned out Robb's. Robb had snuck from his chambers and made his way to the hall. He got there just in time to see Roose stabbing his twin. After a split second of grief, Robb saw red. The Stark temper seemed to grab hold of him and not let go. Unsheathing his sword, Robb ran into the room, slicing through anyone and everyone who got in his way. Somehow, the remaining twin managed to save his mother and escape from the Twins. He knew they'd have to hide for a while, but he vowed revenge on the Freys, Lannisters and Boltons for what they'd done. They would pay for the lives of his brother and wife.