Blondeau hates evening lectures. His students would never suspect, but he, too, has a life outside school, and likes having dinner once in a while.
He puts his notes away and prepares to go home, but stops when he sees a student still sitting in the darkened room, his head on his arms. Blondeau walks over to him. It is Pontmercy.
When he sleeps, Blondeau cannot see his dark, exhausted eyes.
He strokes the boy's hair a few times before waking him and sternly sending him home.
His students would never suspect, but he is younger than they think.
Actually, Blondeau/Laigle would have been more improbable. But this is what I wrote.