Tess squares off against Lionel on the episode "Scion." They battle over the name Luthor.
It's Conner Kent! As this photo makes clear, the character played by Lucas Grabeel will be revealed to be Superboy on a final season episode of Smallville.

Smallville Season 10 Episode 16 Quotes

Lionel: You can't hide Alexander from me forever.
Tess: I'm saving him from an encore performance of Daddy Dearest.

So it's not just the Luthor males who like secrets.