Andrea Libman has stated that Fluttershy has a brother, probably a younger sibling identified with Pop Fly, a young male pony who sings Last Year I Got Coal for Christmas on It's A Pony Kind of Christmas album.
Pop Fly will appear on Friendship is Magic (season 6), but will his human version appear in the Equestria Girls franchise, particularly My Little Pony Equestria Girls: Legend of Everfree?