Introducing a boy, a man says, "He is the son of the brother of my grandfather's son." In this family relation puzzle, how is the boy related to the man?

Introduction / Context:
This verbal reasoning question has a layered description involving a grandfather, his son and that son's brother. Finally, a boy is identified as the son of this brother. The goal is to determine how this boy is related to the man speaking. Such questions test your ability to decode expressions like brother of my grandfather's son and then link them back to the speaker in a clear family tree.

Given Data / Assumptions:
• A man is speaking about a boy.• The boy is described as "the son of the brother of my grandfather's son."• My grandfather's son is, in standard reasoning convention, taken as the man's father unless explicitly stated otherwise.• The brother of the man's father is his paternal uncle.• The son of an uncle is a cousin.

Concept / Approach:
The layered phrase must be unpacked from inside out. First, my grandfather's son is assumed to be the man's father. Then, the brother of my grandfather's son is the man's paternal uncle. Finally, the boy is the son of this uncle. The son of an uncle is always a cousin of the man. Therefore, the boy is related to the man as his cousin. This follows the common pattern used in many reasoning questions where the focus is on distinguishing between brothers, cousins and uncle–nephew relationships.

Step-by-Step Solution:
Step 1: Let G be the man's grandfather.Step 2: The expression my grandfather's son is interpreted as the man's father, F, under the usual exam assumption.Step 3: The brother of my grandfather's son is the brother of F, which is the man's paternal uncle, call him U.Step 4: The boy is the son of this uncle U.Step 5: A child of your uncle is your cousin.Step 6: Therefore, the boy is the cousin of the man.

Verification / Alternative check:
We can sketch the family tree starting with G at the top. G has at least two sons: F (the man's father) and U (the man's uncle). The man is a child of F. The boy is a child of U. Looking at the tree, the man and the boy share the same grandparents (G and his spouse) but have different parents. This is the classic definition of first cousins. No other close relation, such as brother or nephew, matches this structure without changing the given description.

Why Other Options Are Wrong:
Brother: Brothers normally share both parents. Here, the boy is a child of the man's uncle, not of his father.Grandfather: The man is in the same generation as the boy, not one generation above.Nephew: A nephew would be a child of the man's brother or sister, but the boy is a child of his uncle.Uncle: An uncle would be a sibling of the boy's parent; here, the man and the boy are both children of siblings.

Common Pitfalls:
Candidates sometimes misread the phrase my grandfather's son as someone other than the father and end up misidentifying who the uncle is. Another common mistake is to treat any child of an uncle as a nephew, when in fact the relationship goes the other way: the child of your uncle is your cousin. Keeping the generations aligned and clearly distinguishing parent, uncle and cousin roles is essential to solving such problems reliably.

Final Answer:
The boy is the man's cousin.