Greetings Chaim, My Grandmother was Jewish , i was circumcised by a Rabtbi on the 8th day, yet my mother is a Christian women ! what does that make me ? The Jews in Russia had take Russian surnames under Russification by the Czarist mamzers !
First, I hardly think Prokhorov identifies as a Jew, even if he is halachically Jewish.
Second, a man can be born to a Jewish mother, yet be uncircumcised. However, I
believe he cannot be halachically Jewish without a circumcision. To be halachically Jewish, he must be ritually circumcised. Under extenuating circumstances (no pun intended)--such as during times of persecution, etc.--a brit milah can occur at any point. Also, to be buried in a Jewish cemetery, a man must be circumcised. If necessary, one can even be circumcised in death (as odd as that sounds) to ensure proper burial. I think this is to ensure a place in ha-olam ha-ba.
If anyone knows anything to the contrary, please let me know. I believe I am correct, but not 100% certain.