The Ones Lost; Fabled, revered even, as if legend. Because only one met them, long ago.

The Empress was forth-giving with their accumulated scientific knowledge that she saved from oblivion, but she was always tight-lipped about them otherwise. Her ponies only ever got an inkling as to why, and little more from her.
The only ponies that she was frank and open about them to; were the other princesses, her family of sorts.

Geology yields new developments, understandings, and often surprises... archaeology is one of them

Whether this is alt-universe/canon or not, I haven't decided. Maybe, just a what-if? Either way, this takes place after parts 1-3 by a few centuries.

This story is a sequel to The Unknown Daughter's Reunion:Part 2

More than a year has passed since that fateful night at the castle in Canterlot; The night the ruling party of nearly Eighty years Ended abruptly.

Scrambling to fill the void left behind, ponies did their best and worst in its place.

Times are harder than they used to be, corruption is reigning.
Tyranny isn't confined to one form like it used to; It's lesser, but seemingly everywhere now.
In the cities, ponies are afraid to speak too loudly, for fear of what those words usually draw.

Equestria needs the Stable rule of the princesses Back. But how can they turn this tide set in motion by the last ruler?

She wasn't born a princess, a pony, or even a she.
He adapted. It was either that, or crumble into dust.
'When in Rome' the phrase went. Even when the proverbial 'Rome' was built by quadruped equines.

The universe had a purpose for him. Or perhaps another universe did, and bartered?

Having escaped the fate that the entire crew met by no actions of his own, there was no going home, only forward. His new life was about to begin again, in so many ways.

This story comprises of the non-anthro ponies of Equestria, and what our main character became, thanks to them...
Though they had no idea he was even there, and had saved his life. At least, in the beginning, they didn't.

In her life she's seen incredible things; A planet of pegasi, A world of alicorns; Connecting the princess sisters to a now-frozen world, and the magic that got them to Equus before it became entombed in ice...

As well as another space-faring species; That was less than friendly...

Her story is known, her defeat & destruction, and Princess Luna's happy ending...
Though, It in fact was not the end, just the beginning for Nightmare. As those that don't perish, often grow. Whether it's for good or ill is dependent upon the circumstances. These particular circumstances resulted in her becoming a complete pony of her own. Ever thankful of the new friend that gifted her that which she was missing, she persevered.
Into the future that she had built, the ponies that she brought into the world, the new family she made, and eventually the 'empire' (collection of colonies really) that her ponies forged amongst the stars. Far far from Equus.

However, with such growth comes longing. Ponies have an inherent desire to see their families, old and new. Now that she is one, the desire to really know them and love them has long awakened.

'Since Mother and Auntie are alicorns, they must still be alive out there...somewhere?'

With so much that she needs to apologize for, so much to say, so much to know... the day she can see them again just cannot come soon enough. However, it's been more than 9 centuries now, that they thought she was only a thing, and destroyed at that.
Her wait is at an end, though there are always bumps in the road of life.

Though this story is set upon Earth, there are only ponies there now. The world 'building'(unwritten prequel) is a slightly apocalyptic one. Which could even be considered a bit of Nightmare's penance; to have to helplessly witness the end of a civilization (and side step being swallowed up by), in order for her to get a second chance & a clean slate to make her own future. Not everything was lost of them however. After all, where would the idea's of advanced technologies have come from otherwise?
Prequel here: The Early Days

This story takes place many centuries after, in better days.
Part 1; is the lead up to the reunion, and world building. The other princesses do not yet appear (tags adjusted). Also re-rated teen due to married couples (slight comedic romance)