Originally the released date was March 3, 2015 (the same day The Favorite was scheduled to be released), before The Heir, but was cancelled late December, 2014.
Instead of this book, the bindup of The Queen and The Favorite, together with the other two novellas (The Prince and The Guard) and extra content was put in a new book, Happily Ever After. It was released October 13, 2015.
In The Queen:
In The Favorite: