The Royal Diaries series does not have a new book coming out soon. The latest book, Catherine: The Great Journey (Book 20), was published in December 2005.
The first book in The Royal Diaries series, Elizabeth I: Red Rose of the House of Tudor, was published in June 1999.
The Royal Diaries series primarily falls into the Historical genre. This middle grade series was written for ages 8-12, but can be enjoyed by older readers as well.