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?
James Potter (series): The James Potter series is an unofficial sequel-series of J.K. Rowling's Harry Potter universe, written by G. Norman Lippert. Harry Potter and the Deathly Hallows: Harry Potter and the Deathly Hallows is the seventh and final novel of the "Harry Potter" series, written by British author J. K. Rowling.
G. Norman Lippert