There I saw this portrait by Frédéric Bazille, of his friend Pierre-Auguste Renoir. It was painted in 1867. They were close friends who met when they followed drawing classes at the studio of monsieur Gleyre. Here they also met Claude Monet.
The casual pose stands out, it shows that this is the real Renoir, like it was a snapshot. Later that year, Renoir also painted a portrait of Bazille.
(I got this information from the exhibition catalogue)
Anyway, I like this portrait very much.
I decided to look up the other portrait as well, and this is it:
Frédéric Bazille working at his easel, by Pierre-Auguste Renoir, also 1867.