Letter dated 8.1.1820 from Niels Rosenkrantz to Irgens Bergh, cf. Sass: Op. cit., II, p. 2 (“Thorvaldsen has almost finished the busts of the Princess and her sister. Those of the King and the Queen as well. The work is quite successful.”)
Else Kai Sass: Thorvaldsens Portrætbuster, Copenhagen 1963-65, Vol. I, p. 22, 470; Vol. II, p. 2-7, 10, 17, 180, 182.