After Twilight had become a princess, she stayed in Canterlot, eventually bringing her friends along, the only pony who hadn't come was Fluttershy. She had stayed to look after her animals, but she promised to visit whenever she could, the last few times she's come to visit, she noticed that her friends were... Changing, but could not put her hoof on it, when she comes for her next visit, she'll find out.