Another response: I would say the fellow
on the left is not McClellan. He was born in 1865 and that man is
not 35ish. The man on the right has a moustache and I don't believe
McClellan had one ever. It actually looks like Andrew Carnegie.
He was in England quite a bit about that time, donating libraries and such.
(later:) G.B. McClellan did not escort Jones' body back from Paris, Admiral Charles D. Sigsbee did. He had a moustache but no beard.