An asteroid is on course to obliterate Equestria. In the final moments, a mysterious spacecraft visited the planet and scooped up two of every creature. The two earth ponies that get picked to repopulate their species are Button Mash and... his mother.
Whoops.

Maybe the clueless colt should have been paying more attention in sex-ed, rather than playing video games.

Cover art made by https://www.deviantart.com/natt333

Tags: Incest, obviously. And just a tiny sprinkling of proxy Non-Con, similar to the Last Unicorns. Also, Button isn't a foal.