Okay, we know that Mrs. Petrelli is Sylar's mom now, right, but we don't know who his father is. All we know is that he was adopted by a woman who collects trinkets and a father who's a watchmaker.

 

Well, I think Sylar's father is Kaito Nakamura, or Hiro's dad. It was hinted in Season two that Mrs. Petrelli and Mr. Nakamura where more than just friends. Why? Because they secretly had an affair and had Sylar.

 

Which means that the ultimate serial killer is not only related to Peter, but Hiro as well.