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.
Another response: The man on the left looks
very much like Lord Strathcona (Donald Smith) , a railroad magnate and
politician who spent most of his life in Canada and was also known for
equipping a Boer war regiment as well as many other accomplishments and
acts of plilanthropy. He was also appointed Canadian High Commissioner
in London in 1896 and died in England in 1914. https://en.wikipedia.org/wiki/Donald_Smith,_1st_Baron_Strathcona_and_Mount_Royal