It was a beautiful morning in Canterlot. The birds were singing, the castle staff were bustling about their duties with a good cheer, and the sun was shining brightly. Which was a tad unusual, as Celestia was still sound asleep. Those that were in a position to notice the discrepancy simply shrugged it off; it would not be the first time that Celestia had woken up just long enough to nudge the Sun above the horizon and then fall right back asleep. It was probably the oldest running joke in Equestria that the Princess of the Sun was, ironically, NOT a morning pony.

Celestia grumbled and stirred as the first morning's rays finally made their way through the mountain of pillows and sheets to her eyes. With considerable effort she swam her way up through the layers till her tousled head poked up into the open air. She regarded her regal chambers with bleary eyes..... "bleagh," seemed to sum up her feelings on the matter.

She blinked, rubbing her eyes with one free hoof. Something was not quite right. No, not the Sun--- it wasn't the first time she'd raised it and then crashed again; didn't look to be more than an hour past sunrise, thank goodness she hadn't overslept long, then.... no, something else. Maybe several somethings. The room, especially around the bed, seemed to be in more disarray than usual. There were odd articles of clothing strewn about, and what looked like several half empty bottles of....something or other lying on the floor. Some of the clothing strewn about looked rather lacy and -- fishnet stockings?  Since when did she own fishnet stockings? And that bra over there certainly wasn't....

....wait. What?

Celestia found herself experiencing something that no thousand year old royal Princess, with all the accompanying years of experience and wisdom, should ever experience: deepening befuddlement. She found she rather didn't like it.  Her head, she noticed, was throbbing; her mouth tasted like it was full of fur, too. Her discomfort grew. The bedsheets were all sweaty and manky, and there was this heavy, almost...glandular aroma, like....

Her thoughts derailed completely as the blankets next to her stirred. Alarmed, she scooted back to the far side of the bed-- just as the tousled head of the Princess of the Moon popped out from under the pillows. Celestia's little sister, annoyingly enough, WAS a morning person; She was wide awake almost immediately, and looked around her sister's room in rapidly growing alarm. "Celestia, what am I doing here?" She asked. "And why is thine bedroom in such a state?" She regarded the half-empty bottles and scattering of undergarments and other questionable debris with widening eyes. "--Is that a studded collar hanging from thine bedpost?" She pointed with a timorous hoof. For the first time Celestia noticed that several of the items strewn about the room incorporated buckles, straps, and quite probably a very long and unsettling explanation from their owner about their purpose.

Luna paused. In a voice far too small and faint for the normally Wagnerian alicorn, she said, ".....and why are the sheets all sticky?"

There was a moment of silence, a pause not so much pregnant as making its way to the car for the trip to the hospital while its husband ran around frantically looking for the keys. The two royal sisters slowly scooted away from each other and off the bed. Celestia quickly got to her hooves and looked around; her normal expression of benevolent serenity couldn't have been farther away. "I don't know what is going on," she said in a tone of voice that would have made Queen Chrysalis surrender on the spot, "but when I find out..."

Luna prodded the bedclothes with an apprehensive hoof. "....it appears to be maple syrup...."

"I have seen-- and done-- my share of pranks," Celestia continued, "but this crosses every possible line that I-- Luna? Luna, what's wrong?" There was no answer. The lunar princess simply stood frozen on the other side of the bed, forehoof raised in mid poke, Her jaw slack as she gazed with wider and wider eyes at Celestia. Her pinprick pupils flicked up, down, up, down again... then with a gagging, retching noise she spun and galloped from the room as if all the fiends of Tartarus were hot on her heels.

Baffled, Celestia stared after the vanishing cloud of dust, then staggered to the royal bathroom. She realized that something was off about herself; her weight seemed to shift differently and....her body felt wrong somehow. sweet Light, what had happened last night?

The bathroom at least was still normal; a spacious chamber adorned in fine marble and gold fixtures, with all the amenities a pony could wish for. There did seem to be, she noted in passing, a slightly larger selection of bathing oils and lotions than usual. At least she assumed they were bathing oils and lotions.... she trotted past the shelves and stepped in front of the full-length mirror adorning the wall, and gave herself the once-over.

And froze in slack jawed shock at what met her eyes. She stared down at herself in horror; some time in the night, between her going to bed and waking up this morning, she had received some rather radical changes to her undercarriage.

To be brief, she was now, quite explicitly, a stallion.

Well, not entirely a stallion. Further personal investigation revealed that certain other... things... were still present as well, and likewise there were no---

A high pitched sound, like someone strangling a mouse, escaped Celestia's lips. As she stood there, staring down at the abomination wrought upon her, a dark form coalesced into shape in the mirror. Slitted green eyes, midnight black coat, wings as graceful as a swan and as sharp-edged as sin, armor of silver and a mane of stars gathered together, and the visage of Nightmare Moon gazed out upon the world from Celestia's bathroom mirror. The villainous alicorn chuckled malevolently. "ahhaha, at last, I live again! It took ages for me to gather together the wisps of my power, and patiently waiting in the mirror realm-- but now at last, you have fallen into my trap, Celestia! Soon, I shall rule, and the NIGHT--- Shall Last--- hello? Hello, are you listening?"

Celestia didn't reply. Nightmare Moon stepped forward in the mirror and craned her neck. "Pay attention, you foal! What the devil are you looking oh WHAT the HELL?"

There was a brief eternity as the Princess and the would-be usurper both stared at the newest addition to the royal family. Nightmare Moon finally straightened back up and stared off into the middle distance. Her expression was unreadable. "That's it, I'm done. I'm gone, I am outta here. Forget this." She vanished from the mirror in a puff of cosmic discombobulation.

A moment later Celestia found her voice. Her scream blew out all the windows in the tower.

***

On the far side of Canterlot, in a seedy pub on the outskirts of the city, there was a rush of wind and a clap of thunder. The proprietor found himself nose to nose with the Coregent of equestria, Princess Luna. "ALCOHOL!" she bellowed at him in the Royal Canterlot Voice from the other side of the far too narrow bar. He waited a moment for his mane to settle and the bottles behind him to stop rocking. "Alcohol, y-your highness?" he croaked.

"YES! ALL OF IT!"

The bartender cleared his throat, composing himself. "According to the decrees of Faust the First, there are no alcoholic beverages served in---"

"Oh cuttest thou the crap, barkeep," Luna snapped. "Faust didst decree that ale and wine did not exist, but she didst also decree that there wast no such thing as steam engines nor electricity. Tis nobody that is fooled, lest thou thinkest that our loyal subjects spend all cider season drinking foamy mugs of water. Fetch thy fruit of the distillery NOW!" She slammed a hoof on the bar hard enough that furniture across the room danced.

The bartender said not another word; he hastily lined up a half dozen bottles on the countertop, each discreetly labeled--- there was a "root beer", "sarsaparilla," "lemonade," all in colors never seen before in such beverages, and a "Salt Lick" that was suspiciously liquid in form---- in front of the distraught princess and made himself scarce. Luna seized the first bottle (a "ginger ale" quite lacking in ginger), pried the cork out with her teeth, and poured herself a double without benefit of the shot glass.

A misty dark form coalesced in the mirror behind the bar. "so there you are," Nightmare Moon said.

Luna started, then got to her hooves, glaring. "So, villain! Thou hast returned! Twas THY doing that this day---"

"Oh gawds and little green apples, don't start that," Nightmare Moon said, facehoofing. "Not after what I've seen today." She gagged slightly. "Just shut up, sit down and PLEASE tell me that's forty proof in front of you."

Luna sat down, staring suspiciously at the spectre. "So thou art not responsible for my sister's...." she shuddered all over "condition?"

"So you saw it too, huh? Oh come ON Luna, do you think, in any possible universe in all of existence that there is one where any of my plans for making the Night Eternal involve giving your sister a weiner?"

"Don't say it!!"

"That bad, huh?"

Luna slumped on her stool, her eyes haunted. "Two words for thee, villain: MORNING WOOD."

The pregnancy rate for pauses gained another statistic. The mirror-bound wraith shivered all over from hoof to wingtip in atavistic revulsion. "Set up those shot glasses, girl." Luna meekly obeyed. The Nightmare eyed the row of shot glasses-- or rather their reflections--- with a practiced eye. "okay, start pouring."

"When shalt I stop?"

"When neither of us can remember our bleepin' NAMES, much less what happened today." The Nightmare grabbed the first mirror-shot in her hoof and slugged it back.