I CAN EXPLAIN!
 
So basically after Xander was born Herobrine had to leave for the sake of their lives; So Herobrine erased any memory of him from Trixie’s memory. A few years later, Trixie bumped into Prince BlueBlood at a thing in PonyVillie and got to know each other. When they realized they liked eachother; They got married. Couple months later, Trixie gives birth to their daughter; Mistic Gem. She enjoys hanging out with her older half brother Xander. I added Xander into the picture because he’s the son of Trixie and he’s still part of the family.
 
Xander & Mistic Gem - Me  
Price BlueBlood & Trixie - Hasbro  
Bases - SelenaEde