The Second. Expunged.

"No one ever spoke about of those two absent brothers. Their separate tragedies had seemed like aberrations. Had they, in fact, been warnings that no one had heeded?" (from D. Abnett's "Lightning Tower").

Yes, folks, this is it. The primarch of the Second Legion. Of course, his apperance is completely my "invention" because there are nor images of him nor more detailed information.