Lieutenant in the Russian Imperial Cavalry Regiment, and second cousin to the composer (b. 1862; d. 1931), born Georgy Pavlovich Kartsov (Георгий Павлович Карцов).
Georgy was the fourth child of Pavel Kartsov and his wife Aleksandra (née Tchaikovskaya). On 7/19 January 1885 he married the opera singer Aleksandra Panayeva (1853–1942), who was a close friend of Tchaikovsky's.
Correspondence with Tchaikovsky
One letter has survived from Tchaikovsky to Georgy Kartsov, dating from 1888, and has been translated into English on this website:
3 letters from Georgy Kartsov to the composer, dating from 1887 and 1888, are preserved in the Klin House-Museum Archive.