User blog comment:B214/Volume 22 spoilers/@comment-25262334-20160720010158/@comment-25262334-20160720013901

'''Sincerely, there isn't too much female characters that fit description: 1) Good rated queen. 2) Interested in Issei's grown up. 3) Devil. And if we put aside low possibility of her being new character (which would really make no sense by given situation), then most likely possibility is that she is Grayfia in disguise. '''