Might try to restart this topic...
ALEXANDER I's ILLEGITIMATES
For comparison, ALEXANDER I of RUSSIA:
I have managed to find pictures of Sophia Naryshkina and Emanuel Naryshkin, two of the supposed illegitimates of Alexander I by Maria Naryshkina (nee Czetwertyński-Światopełk).
Sophia seems to be fairly clearly the daughter of Alexander I, but Emanuel is a more difficult proposition.
If Lawrence's portrait is accurate and Alexander I had the somewhat squished, bent nose, then Emanuel (who also has that nose type, as seen in the provided photo) is probably his son.
However, not all paintings of Alexander I give him the same nose...
For comparison, here are Dmitri Naryshkin (husband of Maria Naryshkina) as well as his elder brother, Alexander, and some of Alexander Lvovich Naryshkin's sons (Lev Alexandrovich Naryshkin & Kirill Alexandrovich Naryshkin):
DMITRI LVOVICH ('father' of Emanuel)
ALEXANDER LVOVICH ('uncle')
KIRILL ('cousin', brother of LEV)
So does Emanuel *look* like he is Alexander I's son or Dmitri Naryshkin's son?
In the meantime, I have had no luck finding portraits of any of the other supposed illegitimates of Alexander I.
GD CONSTANTINE PAVLOVICH
However, I have managed to discover portraits of the family of Constantine Pavlovich's illegitimate son, Paul Constantinovich Alexandrov.
Paul Constantinovich Alexandrov
GD Constantine Pavlovich of Russia (father)
Josephine Friedrichs (his mother)
Alexandra Pavlovna (his daughter)
Prince Dmitri Lvov (his son-in-law)
All from this site:http://sergekot.com/germanskoe-posolstvo/