This picture from ten volume The Photographic History of the Civil War edited by Francis Miller (1911) highlights an unexpected gathering of former Confederate generals, including Robert E. Lee,  and a few former Union generals such as John Geary and Lew Wallace that occurred in White Sulphur Springs, Virginia in August 1869. This was probably the first photograph of a “Blue-Gray” reunion. For full details, consult Miller’s volume 10 (Armies and Leaders) at Google Books, and see especially p. 4.