Artist's comment:

Celestia had a hard pregnancy. Not physically, but emotionally. She would have panic attacks, feel insecure, and built a wall with everyone — seeming depressed. During the time, most would only see little glimpse of her, normally wearing some type of fabric. (keeping her pregnancy hidden from other's eyes. She couldn't handle questions about the father) The only one who could truly go near her was Luna since her sister was one of few who knew about her relationship with Sombra. But even then Celestia was a little distant to her sister. She did have one room in the castle that felt completely safe. The room that held 'his' broken mirror piece.

After Star was born Celestia still kept the child a secret, but some of the castle staff knew of her. It took nearly three years before Celestia announced her child to the public. (some citizens believe that Star was adopted by the princess in case they needed another royal figure. Most never asked about the father, not wanting to bring up the subject to a princess)