"Sister! What are you doing?"
Celestia and Discord broke apart in an instant. Celestia was startled, but Discord looked positively shocked. "Luna! I-It's not what you think!"
"She's...she's an alicorn," Discord observed in disbelief.
Celestia whipped her head around at Discord, feeling herself being caught in her lie. "N-no! I-I mean..." she trailed off, looking into Discord's eyes. They were filled with disbelief, as if he was debating with himself about what he was really seeing.
Then the disbelief turned to anger.
"Discord, no!" Celestia objected, throwing her hooves around him, trying to form an apology.
"You...you lied to me!" Discord concluded, throwing Celestia off, "You're not the last the alicorns!"
"What?" Luna interjected, eyes darting to Celestia in confusion.
Celestia looked back and forth between the two. They both looked at her as if they were expecting her to say something, but she was at a loss, "I..." she said, a catch in her throat.
Discord's gaze hardened, and he simply shook his head. He began turning around.
"Discord, please!" Celestia begged, "Luna is an alicorn too, yes, but we're the last two! I didn't lie to-"
Discord spun on his foot, cutting her off midsentence, "You said you were the last of your kind, like me. You said you understood me. You said..." Discord trailed off, his expression changing. He looked as if someone has just stabbed him in the heart, "You said you loved me..."
His expression hardened again, "Well I guess that was a lie too," and he spun on his foot, walking away.
"Discord, no!" Celestia screamed, trying to chase after him.
Without turning his head, Discord snapped his fingers, and a glass wall appeared between him and her. She collided with the wall, pounding on it with her hooves. She tried to make her way around it, but it grew to follow her. "Discord!" she yelled in futility, but she could only watch as he walked further and further away. The plants around her began to darken and wither away, but she gave them no notice, only watching as Discord's figure grew smaller and smaller.
Tears spilling out of her eyes, she rested her head against the wall, choking back a rising sob, "I'm sorry," she whispered, weeping.
Luna, unsure of what just happened, tried to put a hoof on her sister's shoulder, failing to console her, "Is this why you've been absent for so much time? You've been seeing him?"
Celestia didn't look up, but nodded.
"What was he?"
Celestia looked up, sniffling and wiping away her tears, "He's Discord, a Draconequus."
Luna's eyes widened in surprise, "You mean from that old filly's tale?" Celestia nodded, "But how's that possible? There aren't supposed to be any of them left?"
"There aren't," Celestia agreed, leaning her head against the wall again, "He was the last,"
Luna began making connections, "So you said you were the last alicorn? To sympathize?"
Celestia nodded, ashamed of what she'd done, "But now..." her mouth closed, quivering, and she began crying again.
Discord seated himself upon his favorite stump, eyes closed in mediation. All around him, the plants began to wither and darken, twisting and warping into gnarled, chaotic shapes. It was his magic that had made the forest flourish, it was as much him as he was, and now it was dying.
She lied to me, Discord thought, his eyes screwing tightly Her and that other alicorn, they may or may not be the last two, I don't know, that could have been a lie in it's entirety. But, lie or not, they have each other. I have myself.
And what am I? he asked himself.
His eyes opened, and they were filled with a new fire; a steely determination.
"I am Discord," he announced, "The spirit of Chaos. I am the harbinger of disharmony."
His eyes turned to the left, the direction in which the pony city was, where the pony princess ruled. She lied to you, he told himself, she deserves what's coming to her.
He nodded in agreement with himself and stood up, clenching his fists, "I am the bringer of perfect chaos," he repeated. He could already see the fire, he could already hear the screams, "So that's what I'll do."
With only a slight hesitation in his step, he unfurled his wings and flew away.