"His name is EGGMAN, Cy Dra! He will never be acknowledged as Robotnik by SEGA of Japan!" *Opens Sonic Unleashed manual* Dr. Eggman (AKA Dr. Robotnik). *Shows interview on SA2 Battle* End of argument.
Okay, yeah! That makes sense! 'Cause if Gerald's his grandfather, then there's an unknown father in there somewhere, which Shadow would be the "brother" of.