Introduction:
Arun and Rajesh are two individuals mentioned in the statement, and the relationship between them needs to be determined. The statement says that Arun tells Rajesh, "I am the son of your father, you are not my brother." Based on this information, we can analyze the relationship between Arun and Rajesh.

Explanation:
To understand the relationship between Arun and Rajesh, let's break down the statement and consider the possible scenarios:

1. Arun is the son of Rajesh's father:
- If Arun is the son of Rajesh's father, then Arun and Rajesh share the same father.
- In this case, Arun would be Rajesh's half-brother, as they share a common biological father but have different mothers.

2. Rajesh is the son of Arun's father:
- If Rajesh is the son of Arun's father, then Arun and Rajesh share the same father.
- In this case, Arun would also be Rajesh's half-brother, as they share a common biological father but have different mothers.

3. Arun is the son of Rajesh's mother:
- If Arun is the son of Rajesh's mother, then Arun and Rajesh would not share the same father.
- In this case, Arun would be Rajesh's stepbrother, as they have a common mother but different fathers.

4. Rajesh is the son of Arun's mother:
- If Rajesh is the son of Arun's mother, then Arun and Rajesh would not share the same father.
- In this case, Arun would also be Rajesh's stepbrother, as they have a common mother but different fathers.

Conclusion:
Based on the given statement, we can conclude that Arun and Rajesh share at least one common parent. Depending on the specific scenario, they can be either half-brothers or stepbrothers. Without additional information, it is not possible to determine the exact relationship between Arun and Rajesh.

Sister