Family Relations

Step 1: Analyze the statement.
The woman says, "His brother's father is the only son of my grandfather."

- The only son of her grandfather is the woman's father.

- The father's son is the woman's brother.

Therefore, the man being introduced to the husband is her brother. So, the woman is the sister of this man.

Step 2: Conclusion.
The correct relationship is that the woman is the sister of the man, so the correct answer is 3. Sister.