"Arthur's great-uncle" is not an official name.
Arthur's great-uncle
Great-uncle Read
Gender Male
Animal Aardvark
Family Thora Read (sister-in-law)
David Read (nephew)
Arthur Read (great-nephew)
D.W. Read (great-niece)
Kate Read (great-niece)
Thora's brother 1 (brother-in-law)
Thora's brother 2 (brother-in-law)
Thora's brother 3 (brother-in-law)
Loretta (niece)
Bud (nephew)
Ricky (great-nephew)
Monique (great-niece)
Loretta's daughter (great-niece)
David's brother (nephew)
Bonnie (niece)
Sean (nephew)
George (great-nephew)
Job Owner of a cheese shop

Arthur's great-uncle was the great-uncle of Arthur Read. Arthur learned about him and two other "uncles"[sic] while researching about his family for a class project.