You know what, maybe you're right, Sergei looks almost the same in the both pictures (if it was indeed the same photoshoot of course - according on Russian sources first picture was taken in 1866, and the next one - in 1864, so it can't be the same session or description is just wrong). Anyway - the same source says that it's Serge.
Funny, I always thought it's Pavel. XD
GD Sergei with GD Ella, little Dmitri Pavlovich and Maria Pavlovna, following the Imperial couple, 1903. (damn watermarks:-()
