With a poof sound of magic, Twilight Sparkle appeared in front of the hall gate of Canterlot royal castle.
(with her teleportation spell of course)

"Hi~I'm here to visit princess Celestia, can you lead me to where she is ?" Twilight politely asked the guards at the door's right.
"Of course! your highness~ princess Celestia happens to be in the main hall right now, please come in."
and so he opened the door behind him, gesturing the allowance of entry. "Thank you, wish you a nice day!" greeted Twilight.
The guard replied with a gentle smile and watched her in, then closed the door immediately, resuming position.

"Twilight~! What brings you all the way here~?" Celestia called with surprise and delight when she saw Twilight came in,
though there's quite a distance from her throne all the way down do the entrance, the favorite student's presence is still familiarly recognizable.
"Well...just some tiny teeny little problems I found in my history studying." said twilight, "not really a big deal."
"But still, I assume it's somewhat important? Because I can't even remember the last time you consult me about your studying. "
Celestia asked back. It's true, Twilight seldom need her assistance in pony since...probably her 4th grade?

"Um...well...it's a bit involved in this year's Hearth's Warming Eve but not really that formally...
it's just that I felt hard to express this problem in letter properly, and that's why I'm here. " Twilight explained herself in a bit of embarrassment, for she hasn't done this for years. "Don't be nervous Twi, I don't mind it at all," Celestia gave back an encouraging
smile while she gracefully trod downstairs from the throne. "In fact I would love you to visit me more often~after all, teleportation spell
DO saves WAY lots more time than writing letters, right?" finishing this observation at perfect timing upon her last step downstairs,
"not to mention I can see you more often~" then they snuggled for greetings.
"I miss you too princess, " Twilight agreed passionately in the snuggle, " been so busy lately I don't have time to drop by here."

Laughter occupies the two for a moment, for they really enjoyed this brief reunion.
"So, back to the point, you just mentioned something about history problems about Hearth's Warming Eve?"
Celestia quoted, "what is it that concerns you?" with a curious look.
"Yes! Well it's my turn to be the director of the festival drama this year, so I was referencing scripts to the actual historybooks and..."
"Twilight," Celestia had to interrupt her, "'it's still summer though, yet you're already onto events on December ? so soon ??"
"I know I know~ it's still 6 months later~ just doing some pre-process check in my free time lately, not overworking~" Twilight ensured.

"Then?" And now Celestia is a bit of confused, because Twilight IS acting kinda nervous...for no reason obvious enough for her to tell.
"Then I found some completely blank years in the corresponding chronicles, and I can't found any documents or historical records
about them, although that won't suggest or change anything about the script but still I just can't let it go as a scholar myself and
(blah blah blah)..."
"Calm down Twilight," Celestia had to break her hysteria, Twilight 's talking too fast to even keep up, so fast it's kind of monologue.
"Speak gently, slowly and simply, forget those routine trivia of yours, what are the 'blank years' you were talking about??" said Celestia.

Twilight took a deep breath, looking up to search for Celestia' s caring eyes, then she started, tongue with much relief :

"The historical fact that our drama script based on is, Chancellor Puddinghead, Commander Hurricane and Princess
Platinum reconciled after all the windigos incident, and this happened at year 495 of the Third Era, right? " paused for Celestia' s confirm.
"Yeah, you recalled it pretty well Twilight, it was 495.3E. so as I remembered~"Celestia nodded, "go on. " Twilight continues her question:
"It's said after the Fire of Friendship is born, the three tribes decided to name this land Equestria and share it as their one united
nation. this is also true, right? " Twilight received another nod from Celestia, only this time she seemed a bit disturbed...
"Okay~ but then this must be somehow strange to The Journal of The Two Sisters, which you and Luna authored of course."
"It clearly stated AFTER Star Swirl the Bearded entrust the royal duties about Sun and Moon to you and Luna, making both of you enthroned, then our Fourth Era started."Twilight concluded, "That leaves a total 5 years blank between the decision & naming of Equestria to actually establishing it! Also, how come it started as if we'll have Republics, but ended up having our Empires nowadays??"

Finally spitting out all that been clouding her, Twilight felt hugely at ease...only until she found Celestia in the complete opposite.
...She even sat down on the floor, her face no longer gentle nor warm like earlier. Instead, princess Celestia gazed at Twilight with eyes
full of sorrow, grief and somewhat...pained emotions? At least that's all Twilight can felt...
"Huhh...." sighed Celestia, "I knew this day will come ever since you become a princess Twilight... but I never thought it's going to be sooo
far sooner than I had expected...way, WAY SOONER than I had in mind, frankly... Your sophistication owed me Twilight...once again..."

Neither had Twilight expected this kind of reaction from Celestia, she thought about many possible ones, but not including this one.

Celestia's voice became so flat and cold, as if she's trying to withhold emotions in, or avoiding any thought about what she said.
Turning around, she murmured a spell and cast a circular magical window floating in the thin air...much like a portal.
"Luna? Are you awake?? We have some royally-serious problem." Celestia called while looking through the window.
As much as Twilight can see, the other side of this window is a dim room, with little glimmer shot between some curtain gaps.
Then there comes Luna, obviously she's approaching form corners of this room which the window can not cover.

"What's the matter sister? You haven't woken me up this way for a long time...(yawn)" Luna mumbled, hoof-robbing her eyes,
She's clearly just waken up, sounds still blurred, with some fuzzy coat and typical morning mane to show so.
"Twilight is here, she...she noticed the lost part in chronicles..." the big princess speaks unemotionally.
"What?!" Luna's eyes shot wide open quickly, telling much surprise she's in. "How come now...how so fast..." but she's not in panick.
"You know what we have to do, meet us in the royal library in 10 minutes." Despite not fully back from her shock, Luna approved,
"Also, clear it out with anypony and express my sorry to the librarian...for this inconvenience, that's all."

Celestia finished, then close the magic window and turn back to face a totally confused Twilight, giving out a chilling vibe.
"Follw me Twilight, I know where to find your answer...if you are sure you really want to know..."
With that said, Celestia turn back again and trot away at once, leaving Twilight freezed from deciding if to follow or not...

Author's Note

We are closing up to the core of my story

Next chapter will be much pacier