Col. John A. McDowell - brother to Irvin?

Andrew Wagenhoffer mentioned to me that he recalls some curious information in a work consulted in days gone - that Shiloh Brigade Commander Col. John A. McDowell was brother to Irvin.
I have not seen that (yet) myself and have been stymied by McDowell genealogy generally. Anyone for the brotherhood of John and Irvin?

How about anyone for a McDowell Cigar?