It was a beautiful afternoon in Equestria. The sun was shining, the birds were chirping, fillies and colts played in the streets of Canterlot. All in all, it was a very good day to relax. Princess Celestia, high ruler of the lands of Equestria, found herself in one of those rare moments when she had nothing much to do.
There were no negotiations needed with a foreign nation, Discord was locked away, and nobody had seen hide nor hoof of either the Changelings or King Sombra's dark essence in a long time. Even her student Twilight Sparkle was off for the day, having sent a friendship letter the day before. So Celestia decided to simply gaze out over the lands from the observation tower, where her keen eyes could see out over much of her kingdom. It was truly a beautiful sight to behold, one that she still loved even after doing so for thousands of years.
"So peaceful," she thought to herself as the sun continued to disappear over the horizon. It was days like this that she was reminded of the joy she felt helping see over such a harmonious land. She would not dwell on the past, back when Discord ruled: those thoughts would spoil the mood and she was content to observe the tranquility.
That was, until a flapping of wings could be heard. It was not one of the guards, the Thunderbolts were at the academy, and Cadence was in the Crystal Kingdom. That meant it could only be one other pony.
"Sister, you are up early this afternoon," she said, not looking behind her as Luna, co-ruler of Equestria and Princess of the Night landed beside her.
"True, but then I felt I must enjoy a glorious evening such as this," the dark blue alicorn said, having finally mastered modern speech patterns and foregone the Royal Canterlot voice.
They sat in silence for a while, before Luna spoke up once more. "Sister?" she asked.
"Hmm? Yes?" Celestia responded, looking down on the smaller royal. "What is it?"
"I have been meaning to ask you a question, something that has been bothering me for some time," Luna said, absentmindedly tracing a circle in the floor with a hoof.
Celestia's curiosity was piqued. "Yes?"
Luna blushed, but continued anyway. "You know I never received all of the schooling one would need as a youngster, basics and all that, since I was royalty and was more concerned with running Equestria than expanding my personal knowledge." She blushed even further.
"Yes?" Celestia said again, wondering where this was going.
"Sister... Where do foals come from?"
If it would have been possible for the eldest sister to complete lose control, the slow progress of the sun would have come to a screeching halt. "...What?" Celestia said, feeling rather confused and not a little bit uncomfortable.
"Where do foals come from?" Luna repeated, looking up at her big sister.
Inwardly, Celestia felt rather ill: this might not end well unless she handled it with the tact and serenity of a princess. "Well, sister, as you know, stallions and colts have different parts from fillies and mares."
"Yes... So?" Luna said. "What does that have to do with anything? Pegasi have wings and unicorns have horns... Is this what you mean?"
Oh boy: this was going to be harder than she thought. "No, no: these are "parts" shared by all pony races. Well, when a stallion and a mare of any of the races love each other very much, they get married. Then the stallion, usually on their wedding night or some time after, puts his... part, in his wife's... part." Oh, if only Discord had escaped, hen Celestia might escape from the nightmare of a situation.
"Then what?" Luna asked, seeming a bit too drawn into the explanation. This could bode ill if Celestia had to be more descriptive. "I always heard mating was something rather enjoyable."
"You have?" Celestia could have choked right there if not for her demeanor. "Well, yes sister, that is true, but mating is only supposed to be between a married couple, or those who love each other very much," Celestia said, hoping her idealized version of the process would not be soon countered by the truth. It wouldn't do good for anyone if Luna decided to go out and... experiment.
"So, they mate, and a baby magically appears? Just like that?" Luna asked. She had not focused on the pleasures of mating, for which Celestia was eternally grateful. The absolute last thing she needed was for Luna to ask her what mating felt like.
"Well, as they... mate, when they are finished the male shoots inside the mare's belly some of his essence, which, given the right time of year, can develop into a foal. From there, the foal grows inside the mare's belly until it is time for it to be born many months later."
"So she pukes it up?" Luna asked. "You said it was in her belly, so when she eats, it eats her food too?"
Celestia almost face-hoofed right there. "No sister: by belly, I meant the area, not the actual stomach. And yes, some of her food goes to the baby, though the method is far too complex for me to explain right now. Anyway, when the time is right, the mare goes to the hospital and gives birth to the foal."
"So that is where foals come from?" Luna asked, her curiosity seeming sated. "Then I assume dragons and griffins come from eggs?"
"Yes, sister, they do. Does that answer your original question?"
"Indubitably, sister." She stood up rather suddenly, and Celestia only noticed now she had completed the sun's arc across the sky. Stars were beginning to sparkle in the heavens above as the moon appeared from its hiding place. "Well, it is my turn to watch over the lands: perhaps you should be getting to bed."
"Yes, quite," Celestia said, mentally exhausted as she stood up and walked off towards her quarters. "I could use a good night's sleep."
As she left, Luna smiled: that had gone better than she had expected. Luna had known of course where foals came from: the library had provided the answers a long time ago. She just wanted to hear Celestia's take on the matter.
"Sleep well, sister," she said to herself, before she resumed looking out over the lands.
Author's Note
Just a short story I thought of. Oh Luna, you irascible little alicorn!