Bullet Points:

- Two film stars are each a father to a son.
- The relationship between the two film stars is not mentioned in the given information.
- Let's explore possible scenarios for their relationship:

1. Biological Brothers:
- The two film stars could be biological brothers, making their sons cousins.
- This would imply that the two film stars share the same parents.
- However, it is important to note that the question does not provide any information about their familial relationship.

2. Close Friends:
- The two film stars could be close friends who have a strong bond.
- They might have decided to have children around the same time or even through surrogacy or adoption.
- In this case, their sons would not be biologically related but could consider themselves brothers due to their fathers' close friendship.

3. Co-stars in a Movie:
- The two film stars might have acted together in a movie where they portrayed a family.
- While they are not related in real life, their on-screen portrayal could have been so convincing that people often assume they are related.

4. Film Star and Son's Co-star:
- One film star could be the father of the other film star's son.
- In this scenario, the two film stars are not related, but their sons are half-siblings.
- This could happen if one film star had a child with another person and the other film star's son acted alongside their half-sibling in a movie.

Conclusion:
- Without additional information, it is impossible to determine the exact relationship between the two film stars.
- They could be biological brothers, close friends, co-stars in a movie, or one film star could be the father of the other film star's son.
- The relationship between their sons would also depend on the specific scenario.