There was one person that Thorax, Pharynx and the other changelings barely mentioned. That person was Thorax's and Pharynx's adopted older brother Beta, who was found in the Hive by them several years ago.

One day, Beta left the Hive and was never seen again, because as much as he wanted to stay with Thorax and Pharynx who he grew to love as his own family, he couldn't stay because of Chrysalis.

After Chrysalis was overthrown by Thorax, Starlight Glimmer, Trixie and Discord, Pharynx offered his brother to go out to look for him, but Thorax always declined his offer, even though he'd happily join his brother in his journey to find their brother, saying that he can't because he has to look out after the Hive.

But, one day Beta returns to the Hive, along with three other humans, and a young griffon that happens to be his adopted daughter.

This story starts right at the beginning of season 8.
I suck at summaries.
My english is not the best, so sorry for every grammar mistake I made.
Rated T for profanity, mentions of death and character death.