Identity:
Guéeau de Mussy was probably a physician.
Life:
Guéeau de Mussy appears to have attended Alphonse Legros's bumps and bruises after Whistler quarrelled with him in 1867. He may have been a doctor attending foreigners in Britain, or visiting London briefly. de Mussy seems to have been a friend or colleague of F. Seymour Haden, and his letter was used as evidence of Whistler's violence, in order to force his resignation from the Burlington Fine Arts Club.