Alright, Twilight and Flash are no longer a thing, which means Asteria is out of the picture too - and in comes, yes you guessed it, Luster Dawn. Time for a little backstory, and by little I really mean little;
 
Princess Twilight Sparkle and Sunset Shimmer had just gotten married a few months back, and one day the thought hit them, they wanted a foal of their own. But, since they both were mares, they had no clue how this would work out.. until Starlight Glimmer and Sunburst stepped in to help them both. 11 months pass, and she's finally here, Luster Dawn. Sunburst and Starlight stay as her biological parents, but she's now in Twilight and Sunset's hooves.