An iTunes preview for the upcoming "My Little Pony: Meet the Ponies of Maretime Bay" book has a preview image including a map of the current Equestrian world. One specific spot on it is a castle that seems to name that new alicorn we saw at the end of Make Your Mark. "Opaline's Dark Castle" sits north of Mareetime Bay, and most people are speculating that this is likely the home of out newest horse villain.
Get more pages below. The book releases on the 13th of September, so we have a bit to go before we find out.
Thanks to Sombra and OrangeFlower for the heads up.