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 "James Potter (series)"): The novel series centers around the character of James Sirius Potter, Harry Potter's son, a character who makes a fleeting appearance in the novel "Harry Potter and the Deathly Hallows".
Relevant evidence: No