two speedlights set-up:
on camera flash to ceiling + off-camera at left and little backward of boy with diffuser pointed to the ceiling also, in manual mode 1/32. I wanted to create impression of sun-light coming through the window from top-left corner of picture.
Postprocessing: Lightroom to b/w and toned.
I know I was bothering him, but I had to use the chance and fix him at work.