What would a Cantonese speaker call a male adult non relative who has adopted them?

The situation is late 1800s China. The character is a Cantonese speaking boy, about 10 years old. He has no family and is taken in by a supernatural being that mentors him and develops a sort of familial fondness.

Is there some form of grandfather or uncle that would be appropriate in this situation? Or is there another more formal title that would be better? I'm a little overwhelmed by the number of different ways of referring to relatives in Cantonese.