Been waiting ages for that letter. It HAD to come.

Bruce wouldn't not support him by knowing him.

Also? Eradicator, maybe? Who... ends up bequeathing the last of himself into 'Country Clark' at the end? Mixing up that old story? Whether or not Clark has to fight for control, or the Eradicator turns face. Maybe hints that the Eradicator was meant to protect 'Superman' all along - but got twisted?