Georgetown Symposium Provides Answers
.... ambiguous, as life itself, but appearing balanced. I'm afraid that the praise for King Boris is greatly oversimplified. "Rescuing Bulgaria's Jews: A 60th Anniversary Symposium."
"Two Bulgarian Clergymen Named as Righteous Among the Nations for saving Jews during the Holocaust."
Frederick Chary appears to be an excellent source.
And thanks to Google, Georgetown, Wikipedia and Yad Vashem.