Over A Thousand Years Ago...
The air was tinged with a mix of unspeakable joy but also unfathomable sorrow as the alicorn princess cradled the infant to her chest, lovingly nuzzling the tiny being's cheeks and was rewarded with the infant's pleased-sounding coos. Only a week had passed since Celestia had given birth to her daughter, a sixteen-hour process that she was certain was going to kill her from how the little unicorn had seemed to drain the very life out of her. The doctor and midwives were understandably concerned with the health of both the mother and the baby but were relieved when both came out of it completely healthy. Initially, as she laid there in terror and agony, a sweaty hoof intertwined with Luna's, Celestia was afraid that her child would be an umbrum like their father but was calmed when she delivered a normal-looking filly.
"It's a girl, Your Majesty. Congratulations!"
The doctor's words rang out in Celestia's head as she peered down to gaze upon the face of her firstborn. Oddly enough, fate had decreed that she'd look like neither of her parents, instead resembling her deceased grandmother Queen Concordia, who'd died years before. Same color coat, nearly identical mane. Only instead of golden eyes, light purple eyes stared up at Celestia.
She's so beautiful, like the most lovely melody in the world.
She remembered thinking when she first held her daughter in her forelegs and decided to name her Cadence, a title her old music teacher would've no doubt approved of.
"My little Cadence. I love you," Celestia whispered to the giggling infant, trying her best to hold back tears.
Through a secret entryway behind her throne and down several tunnels, Celestia clutched the week-old filly to her chest, stopping every so often as to ensure that she wasn't being followed. Ever since discovering that she was pregnant, she and Luna had both become alert to the point of obsession, doubling the number of Royal Guards as well as active Royal Intelligence operatives. There would no doubt be complaints of overtime and an extra expenditure of staff pay but to keep Cadence's existence a secret, Celestia would give up every bit in the Royal Treasury if it meant that her daughter would be safe. She'd rehearsed the lines she'd say to Sombra the next time that they spoke but it still brought a sickening sensation to the pit of her stomach. To even imply such a disgusting action brought her shame but if Luna was right, it would bypass Sombra's empathic abilities and detract him from searching for their child.
Hanging a left, Celestia arrived in a decagonal antechamber, where Luna stood patiently waiting by a cradle made up of sky-blue crystals.
"Are you alright, Sister?"
Peering down at Cadence's sleeping face, she paused to take in every feature, her hoof stroking the pink cheek and feeling her little chest rise and fall. A part of Celestia wanted to yell at Luna that this was her daughter and that she wasn't going anywhere but the stronger, more reasonable part told the princess that this was the only way. She nodded slowly, her hooves stiff and heavy as they carried her to the cradle. She held the foal over it but found that she couldn't let go.
"Celestia, we've talked about this. If the court found out that you conceived a child with one of our sworn enemies, they may see this as an act of treason and demand your removal from the throne. After a few centuries, we'll wake Cadence up from her enchanted sleep and put her up for adoption. Nopony will ever need to know the truth."
"I...you're right..." Celestia agreed and slowly lowered Cadence into the cradle, her small body sinking into the dark blue velvet cushion as a blanket was pulled up to her chin. The foal whimpered slightly but remained asleep, blissfully unaware of the situation developing around her.
"I don't...I don't want to do this," the elder alicorn sniffled, tenderly brushing Cadence's cotton-soft bangs. "I don't want to say goodbye."
Luna placed a hoof on her sister's shoulder. "I know but this isn't permanent. You'll see her again soon." She stepped forward and ignited her horn, lowering the glowing blue extremity towards a gold medal on the front of the cradle.
"W-wait!" Celestia steeled herself, wiping the tears from her face. "It...it should b-be me."
Nodding understandingly, Luna deactivated her horn and respectfully stepped away. Celestia took one last, pained look at Cadence before her horn flared to life and, with a deep breath, lowered it towards the medal, filling it with her magic. Jagged, clear-blue crystal shards emerged from the lip of the cradle, creating smaller crystals that slid upward from the next until they formed an oblong dome over the cradle. Inside, little Cadence slept peacefully. Her horrible task complete, Celestia collapsed onto her stomach and let loose a wail of anguish.
Now...
Celestia peered into the tear-filled eyes of the young alicorn before her, who stared at her "aunt" with the look of somepony that wanted answers but was also afraid of what they entailed.
She really does look like Mother.
The air was thick with tension though nopony spoke; it was clear that they all knew that. In that moment, Celestia felt the centuries press down on her shoulders, now feeling like the old mare that she knew that she was. She sighed and turned away, the words finally leaving her lips after a thousand years of secrecy.
"It's true."
When she faced forward again, Cadence was nodding slowly, biting her lip as she let the confession sink in. More tears joined their kin in rolling down her cheeks.
"And...are you...are you m-my mother?"
There was no turning back now.
"Yes, I am."
Celestia turned to glare at Sombra, expecting a smug grin or a sadistic smirk. Instead, his face was etched with sorrow and rage, his eyes boring into her own as if this was her fault!
"Are you happy now, Sombra? Are you?"
"No, I'm not," came the simple reply. "Are you going to honestly blame me for this?"
"Who else?! You had no right!"
"No right? I'm her father!" Sombra roared, his eyes burning with revulsion.
"No, you're not! You may've helped to create her but you're not her father!"
"Oh, and that automatically makes you her mother? I wasn't around because you and your vile sister had me trapped underground for a thousand years! You gave her up and ignored her until she earned her wings!"
Celestia whirled around, her wings spayed open and ready for attack.
"I was protecting her!"
Sombra snorted, "Protecting her...or yourself? You cared more about your reputation among your subjects than your own flesh and blood! I was more open and honest with Cadence in one hour than you were for her entire life!"
"Stop it, both of you!" Cadence screamed, purple smoke curling from her glowing green eyes.
Both of them clamped their mouths shut as the Princess of Love took in several deep breaths.
Finally, she uttered, "You were both wrong," before turning to Celestia. "You've been lying to me since day one. You made me believe my life was mine. All this time you could've told me the truth but you didn't. Either you felt like I couldn't handle it or that it'd hurt you too much. This is my life and I deserve to have a say in it!"
She then faced Sombra. "It wasn't your decision nor your right to tell me. So why are you here? Why did you come back? Was it just to get back at Celestia? Is this just a game to you?"
Sombra's shoulders dropped, his gaze full of hurt and despondency.
"Cadence...I know that I'm a monster...but I swear to you that I would never do anything to hurt you. Don't you see? I came here for you."
"Sombra," Celestia growled, her horn glowing with a golden light. "Don't you dare-..."
Black crystal columns shot out of the floor, ensnaring her limbs and forcing her onto her hindlegs. She screamed in pain as several smaller black crystals became embedded in her horn, eliminating the golden light and cutting off her magic.
"Celestia!"
Sombra was now a foot away, his own horn pulsating with green energy.
"Don't...threaten...me," he snarled, punctuating each word by baring his fangs at her. "Now, no more interruptions. My daughter asked me a question."
He returned his focus to Cadence, who stood shivering in fear by the display.
"I already told you that I would never hurt you and I mean it. You're my daughter, my own flesh and blood. Now, you asked me why I came here. You see, when I returned to life, I was furious beyond description and ready to deal out vengeance to those who wronged me. Celestia was the first on my list for what I thought was the murder of my unborn child. As I stood above her sleeping form, I wanted to cut her throat."
His tone became more hopeful, his face cheerful.
"And then I discovered the truth. My child lived and was still around all these years later! I realized then that I was no longer the last of my kind. I was no longer alone!"
Sombra's voice boomed throughout the room, his hooves raised towards the heavens as he stood triumphantly on his hindlegs. He then grew quiet and planted himself back on all fours.
"All those years away from you. I missed your birth, hearing your first words, taking you to school. And then it hit me! I could aid you in expanding your kingdom! Why relegate yourself to a princess when you can be a queen?"
His tone became more pleading, more energetic.
"You could have all of Equestria at your hooves, and the lands beyond! How many parents can say that they can literally give their child the world? We can overthrow Celestia and Luna, you and I, end their tyranny and right the wrongs that the alicorns made. There could be true peace and prosperity and it can be because of you. They will flock to worship you."
Sombra laid a feather-light hoof on Cadence's foreleg.
"Please, Cadence. Let me make up for lost time. Let me be the father that I should've been to you. I...I love you."
The green and purple vanished from Cadence's eyes, her natural pink ones staring incredulously at the unicorn before her. In that moment, she longer saw a wicked tyrant or an evil warlock but a sad stallion looking to reconnect with the only family he had left. She felt the sincerity in his voice and despite it seeming insane, she believed every word that he said. But it was not a path that she could take. Bringing her foreleg back, Cadence slowly backed away.
"I can't. I won't help you take over Equestria. I don't want that! I'm sorry but I won't become somepony that my subjects will fear and loathe. I won't become you."
Sombra lowered his head, pain etched into his worn-out face.
"I see. I...I was a fool to think...that you'd want anything to do with me. I thought you would listen to reason. I thought you'd understand."
He stood back up, his eyes full of angry tears.
"But you don't. You choose to live in the false utopia that they created!"
He jabbed a hoof in Celestia's direction.
"The history books say that the umbrums invaded Equestria but the truth is, we lived in settlements long before the other equine races arrived. Celestia's 'sainted' mother ordered our execution, butchering countless stallions, mares and foals! The bat-ponies? Driven from their homelands so that Canterlot could be built on the foundation of their forefathers! The Changelings? Forced into the wastelands to starve to death! Your utopia is built on blood and lies!"
He stopped his rant to acknowledge the sudden pulsing red light of his horn. A grin of malcontent curled his lips.
"Ah, more guests have arrived. Excuse me."
The black crystal doors momentarily split open, allowing Sombra to slip through before they slammed back shut.
"I'll be back soon..."