Introducing a boy, Amar said, 'He is the son of my maternal grandfather's son.' How is that boy related to Amar?

Introduction / Context:
This question involves maternal relations and a nested phrase: the son of my maternal grandfather's son. You must carefully decode the family link from Amar up to his maternal grandfather, then down to the boy. The concept tested is whether you can distinguish between uncles, brothers and cousins when the path to the person goes through grandparents and their children.

Given Data / Assumptions:
- Reference person: Amar. - Amar speaks about his maternal grandfather. - The boy is the son of Amar's maternal grandfather's son. - Maternal grandfather is Amar's mother's father. - Maternal grandfather's son means a son of Amar's maternal grandfather, i.e., Amar's maternal uncle.

Concept / Approach:
The crucial step is identifying who my maternal grandfather's son is. Amar's maternal grandfather is his mother's father. Any son of that man is Amar's maternal uncle, because he is the brother of Amar's mother. The boy is the child of that maternal uncle. Children of uncles and aunts are cousins. Therefore, the boy is Amar's cousin. We must not confuse this with a nephew or brother.

Step-by-Step Solution:
Step 1: Identify Amar's maternal grandfather as the father of Amar's mother. Step 2: A son of Amar's maternal grandfather is the brother of Amar's mother. That person is Amar's maternal uncle. Step 3: The boy is described as the son of this maternal grandfather's son, that is, the son of Amar's maternal uncle. Step 4: A son of an uncle is one of Amar's cousins. Step 5: Therefore, the boy is Amar's cousin.

Verification / Alternative check:
Visualise the family tree: at the top, Amar's maternal grandparents. They have at least two children: Amar's mother and her brother (Amar's maternal uncle). On the next level, the maternal uncle has a son: the boy in the question. Amar is the child of his mother. Both Amar and the boy are grandchildren of the same maternal grandparents but through different children. This is exactly the structure for first cousins, confirming the conclusion.

Why Other Options Are Wrong:
- Maternal uncle: That would be Amar's mother's brother. Here, the boy is the son of that uncle, not the uncle himself. - Nephew: A nephew would be a child of Amar's sibling, but the boy is not described that way. - Brother: A brother would share Amar's parents. The boy shares grandparents but not parents with Amar. - Uncle: An uncle is a sibling of a parent or spouse of an aunt, a generation above Amar, not below or at his generation.

Common Pitfalls:
A frequent mistake is to misinterpret maternal grandfather's son as Amar's father, but that would make Amar's father and mother siblings, which does not match normal puzzle assumptions. Another common confusion is between uncle and cousin; remembering that uncles and aunts are siblings of parents while cousins are their children helps separate these roles. Always work one generation at a time and clearly label each person's position in the tree.

Final Answer:
The boy introduced by Amar is his cousin.