After I followed C.Kunin's tip about Chekhov's autobiography, where a certain Dr. Botkin is mentioned, I discovered that there's an article by Shul'tsev GP (in Russian) about "A.P.Chekhov on S.P. Botkin." Cf. Klin Med (Mosk). 1986 Nov;64(11):143-4.
PMID:  3546930  [PubMed - indexed for MEDLINE]
and Klinicheskaia meditsina 64:11 1986 Nov pg 143-4 MeSH

I happened to be watching an old BBC TV film series with Kenneth Branaugh as "Wallander." Today, in the last episode available on TV, I decided to check about s the actor who plays Povel Wallander (the detective's father), namely David Warner 

It was fun to discover that in 1996 he played a minor role in "Rasputin: Dark Servant of Destiny". He was Dr. Eugene Botkin!.

 

Chekhov's doctor Botkin died of cancer, the Romanov Botkin was shot.

I'd been inclined to bet on Nabokov's choice of the name "Botkin" after the assassinated royals's physician name (as some sort of connection with Charles, the Beloved).Now, with this new Botkin in the overall scenery, I'm not as sure as I was before.