From Natalia's 2016 Facebook post, one commenter noted “Tusya”, to which she replied. Since Barsik is already a known cat, it follows that the grey cat must be Tusya.
Facebook post about Tusya -
https://t.co/eAnBvtM9Gf
X post confirming Barsik -
https://t.co/dRum4F6HLO