A few days after the birth of Rainbow Dash and Bookworm's son, Rainbow Sprinter, they received a visit from Princess Celestia, as they had some questions about their newborn colt's "condition." The rainbow maned mare had Spike send her a letter the day after her son had been born.
Dear, Princess Celestia
Bookworm and I have welcomed our son, Rainbow Sprinter, into this crazy world of ours! We couldn't be happier! But, there's something...off about him. You see...he has both wings and a horn! Does this mean he's an alicorn? Is he royalty? Is he gonna have to go to some fancy school? Doctor Stable said all tests showed him being normal, but I really wanna make sure of that and figured you'd be the best pony to ask. So, if possible, I hope you can come to Ponyville and examine my son and tell us for sure.
Your faithful subjet,
Rainbow Dash Scholar
The princess looked over the young colt for a few moments, eyeing him carefully, then she lit up her horn and surrounded him all over. The rainbow maned colt never cried during this examination, mostly making some giggling and cooing noises. After nearly half an hour, she was finally ready to give her answer.
"I can firmly say that your son is not an alicorn," proclaimed Princess Celestia.
Rainbow Dash and her husband looked at each other for a moment in confusion, not really sure how to feel about the whole situation.
"Then, what's up with him?" Rainbow Dash finally asked. "If he's not an alicorn, then why does he have a horn and wings?"
"Quite simple," began Celestia. "His mother is a pegasus and his father is a unicorn."
Again there was a bit of silent confusion, it was clear Celestia was pausing for dramatics.
"While extremely rare," the princess began again. "I'd say only once in a century or so, it is very possible for parents made up of a unicorn and pegasus to produce what I would call a pegacorn. Young Rainbow Sprinter here merely possesses the physical traits of his parents. I.E. the wings of his mother, that being you, Rainbow Dash, and the horn of his father, that being you, Bookworm."
"So, there's nothing wrong with him?" Rainbow Dash asked in an unusually timid manner.
"Of course not," replied Celestia in a comforting tone. "Your son is perfectly healthy both physically and mentally."
"Does this mean he'll have magical abilities in addition to flying?" asked Bookworm. "I hope that isn't a silly thing to ask."
"It certainly isn't," assured Celestia. "To be perfectly honest, I cannot say what his magical properties will be like. Since he is also a unicorn I can safely assume he will be able to cast some magic, but how effective they'll be is hard to say."
Rainbow Dash and Bookworm let out a huge sigh of relief. While they were reassured by most every other pony that their son was fine, being new parents they couldn't help but have a little panic. Hearing these words from their ruler was the most comforting news they could get.
They later met with their friends at the Golden Oaks Library to tell them all the news.
"A pegacorn, eh?" said Applejack. "Well, that's certainly somethin too!"
"A once in a century type pony is something to be very excited for!" exclaimed Twilight.
"Just being the son of Equestria's best flyer and the author of the Daring Do books made him special," exclaimed Pinkie Pie. "But now he's super duper crazy awesome mega special!"
"And of course he's still quite the little darling," said Rarity.
"He really is super cute," said Fluttershy.
Later that night at her home, Rainbow Dash sat in the living room quietly for a moment, holding her son and simply smiling at him.
"You're better than any Best Flyer Medal, or a million Wonderbolt air shows put together," she said quietly, never taking her eyes of him as he looked back up at her smiling. "You've made my life way more than 20% cooler little guy."
"And I didn't do that already!?" exclaimed Scootaloo, not in bed yet.
"Or me, for that matter!?" exclaimed Bookworm with clear sarcasm.
"Of course you both did!" exclaimed Rainbow Dash. "You've all added a huge a percentage of coolness to my life!"
"And you wouldn't trade it for anything?" asked Scootaloo, huddling next to her new mother.
"Absolutely nothing," replied Rainbow Dash, wrapping her free hoof around her daughter and nuzzling her. "You all are the most important ponies in my life. Nothing will ever change that."