Question: Who wrote an unofficial sequel-series of J.K. Rowling's Harry Potter universe, that enters around the character of James Sirius Potter who makes a fleeting appearance in the  final novel  of the "Harry Potter" series, written by British author J. K. Rowling?
Sentence (from "Harry Potter in translation"): The "Harry Potter" series of fantasy novels by J. K. Rowling have become some of the most widely read works of children's literature in history, with readers of all ages and in many countries.
Relevant evidence: No