Photo of American dignitary in England, c. 1900. Who is he?

Photo of American dignitary in England, c. 1900. Who is he? Click photo for enlargement.
I got a response: son of George B. McClellan, mayor of New York City, 1900, in London on his way to Paris to pick upthe body of John Paul Jones for reburial in USA. Comments?

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.