Cadence burst into the great hall, Twilight by her side, just in time to hear Chrysalis complain.
"Ugh! Why does she have to be so possessive of her brother? [sobbing] Why does she have to ruin my special day?”
Cadence tried not to roll her eyes at the charade. “Because it’s not your special day. It’s mine!” She looked around at the confused ponies assembled there. “She's a changeling. She takes the form of somepony you love and gains power by feeding off your love for them.” She pointed an accusing hoof, eyes flashing with grim satisfaction as she finally outed her imposter.
Chrysalis growled, and in a flash of green fire, took her true form, growing taller, wings changing into buzzing insect wings, her skin turning black and chitinous.
Cadence started forward, headed for Shining, but was stopped by a slam of Chrysalis's hoof. “Ah, ah, ah. Don't want to go back to the caves, now do you? Ever since I took your place, I've been feeding off Shining Armor's love for you. Every moment he grows weaker and so does his spell. Even now, my minions are chipping away at it. Soon, my changeling army will break through.
"First, we take Canterlot. And then, all of Equestria!”
“No. You won't.” Cadence blinked. She’d just been about to say that. She saw Celestia step up behind Chrysalis, who whirled to face the new threat.
“You may have made it impossible for Shining Armor to perform his spell, but now that you have so foolishly revealed your true self, I can protect my subjects from you!” Celestia reared back, the full might of the sun princess brought to bear in a torrent of magical energy that the changeling quickly blunted with a green beam of fire.
Cadence sighed with relief. It was over. Celestia was one of the strongest magic-users in the world. But she stared in disbelief as the changeling matched that awesome power... and pushed back against it.
Her hopes were dashed as Celestia was thrown back to the floor. Twilight and her friends ran out of the great hall as changeling drones broke through and descended on the city.
She rounded on the changeling. What could she do? What more could be done? She started past Chrysalis, up the steps toward Shining Armor. She reached the top just as two drones descended and trapped her hooves in a green, sticky goo.
Chrysalis sauntered over to her, insufferably pleased with herself. “His love for us is so strong.” She grinned at Cadence. “I wonder why...”
Cadence grunted a “hmmmm!” of defiance at her. “For me." And that’s because we do love each other! Whatever you say!”
Chrysalis snorted in disbelief. “You still can’t say it to him, can you?” Cadence turned to look at Shining, and licked her lips nervously. “Twilight and her friends will–”
The doors burst open, and the captive Twilight and her friends were herded into the grand hall by a dozen changeling guards.
“You were saying?” Crysalis asked her with a gloating smile. She turned to the window, laughing manically and watching the drones tear canterlot apart. She didn’t see Twilight crawl over to Cadance and remove the green goo with a short burst of magic.
“Go to him,” Twilight whispered.
She darted over to Shining, reaching out to gently touch his face, a tear rolling down her cheek at his unwavering, green-eyed trance. She felt leaden in her stomach. Why hadn’t she told him? Out of all the chances she’d had, why had she never told him how much he meant to her? All the fear, the doubt, the indecision, why why why had she let it stop her?
She started as he groaned and shook his head, and she felt herself smile for what felt like the first time in years. He was okay! He was... well, everything else was doomed, but he was okay!
“Perform your spell!” Twilight called out.
He tried. He tried alone. She saw how much it hurt him to try. But he couldn’t. “I don’t have the strength to repel them.” He groaned.
He needed her. She reached out to him, clinging to him tightly. “My love will give you strength.”
Crysalis scoffed. “What a lovely but absolutely ridiculous sentiment.”
Cadence shot her a venomous look, then closed her eyes, pouring all the love she’d fought so hard to feel into him, pushing past her false and phony feeling until finally, she allowed herself to feel how she truly love him. She touched his horn to hers, and...
“No! No!”
She peeked an eye open as she heard Chrysalis screech, then opened them both in alarm at the scene around her. Everypony was frozen in place, except for the changeling, who was striding toward her, fury painted on her face.
“You’re still clinging to the lies, Cadence! That is not true love!”
Cadence rounded on her. “What have you done? What’s going on?”
“I’m showing you the truth. I thought you could face it here, but you couldn’t. You brought this on yourself.”
Chrysalis’s horn glowed a deep green, and everything went black.