To find out the author of 'fredrick the great historical novel', one could start by looking in specialized historical fiction libraries or databases. Check for books about Frederick the Great in the historical novel section and see who the credited author is. Another option is to ask historians or enthusiasts of Prussian history if they are familiar with this particular novel and its author.
There are many authors who might be interested in writing about Frederick the Great. It could be a relatively unknown author who did a lot of research on the topic. Maybe it was an author with a particular interest in Prussian history. However, without further research, I can't name a specific author for this novel.