How to handle royalty as authors ??

I want the a king to appear as the author in a bibliography eg 

Charles IX. Book title. Year etc.  

But, his name keeps getting abbreviated to IX, C. as if IX was his last name … 

Thanks in advance 

R

Is “Charles IX” the complete name?  Just wondering as there are different “Charles IX” throughout history.  In any event just treat his name like an organization by adding a comma in the Author field which will then display the complete name:

Charles IX,