According to Kinbote (in VN's novel Pale Fire, 1962, Shade's mad commentator who imagines that he is the last self-exiled king of Zembla), Oswin Bretwit (the Zemblan former consul in Paris) was not exactly persona grata with the new regime:
I, too, was wont to draw my poet's attention to the idyllic beauty of airplanes in the evening sky. Who could have guessed that on the very day (July 7) Shade penned this lambent line (the last one on his twenty-third card) Gradus, alias Degré, had flown from Copenhagen to Paris, thus completing the second lap of his sinister journey! Even in Arcady am I, says Death in the tombal scripture.
The activities of Gradus in Paris had been rather neatly planned by the Shadows. They were perfectly right in assuming that not only Odon but our former consul in Paris, the late Oswin Bretwit, would know where to find the King. They decided to have Gradus try Bretwit first. That gentleman had a flat in Meudon where he dwelt alone, seldom going anywhere except the National Library (where he read theosophic works and solved chess problems in old newspapers), and did not receive visitors. The Shadows' neat plan sprang from a piece of luck. Suspecting that Gradus lacked the mental equipment and mimic gifts necessary for the impersonation of an enthusiastic Royalist, they suggested he had better pose as a completely apolitical commissioner, a neutral little man interested only in getting a good price for various papers that private parties had asked him to take out of Zembla and deliver to their rightful owners. Chance, in one of its anti-Karlist moods, helped. One of the lesser Shadows whom we shall call Baron A. had a father-in-law called Baron B., a harmless old codger long retired from the civil service and quite incapable of understanding certain Renaissance aspects of the new regime. He had been, or thought he had been (retrospective distance magnifies things), a close friend of the late Minister of Foreign Affairs, Oswin Bretwit's father, and therefore was looking forward to the day when he would be able to transmit to "young" Oswin (who, he understood, was not exactly persona grata with the new regime) a bundle of precious family papers that the dusty baron had come across by chance in the files of a governmental office. All at once he was informed that now the day had come: the documents would be immediately forwarded to Paris. He was also allowed to prefix a brief note to them which read:
Here are some precious papers belonging to your family. I cannot do better than place them in the hands of the son of the great man who was my fellow student in Heidelberg and my teacher in the diplomatic service. Verba volant, scripta manent. (note to Line 286)
In his Commentary to Shade's poem Kinbote calls Gradus (Shade's murderer) "Vinogradus" and "Leningadus:"
Such things rankle - but what can Gradus do? The huddled fates engage in a great conspiracy against Gradus. One notes with pardonable glee that his likes are never granted the ultimate thrill of dispatching their victim themselves. Oh, surely, Gradus is active, capable, helpful, often indispensable. At the foot of the scaffold, on a raw and gray morning, it is Gradus who sweeps the night's powder snow off the narrow steps; but his long leathery face will not be the last one that the man who must mount those steps is to see in this world. It is Gradus who buys the cheap fiber valise that a luckier guy will plant, with a time bomb inside, under the bed of a former henchman. Nobody knows better than Gradus how to set a trap by means of a fake advertisement, but the rich old widow whom it hooks is courted and slain by another. When the fallen tyrant is tied, naked and howling, to a plank in the public square and killed piecemeal by the people who cut slices out, and eat them, and distribute his living body among themselves (as I read when young in a story about an Italian despot, which made of me a vegetarian for life), Gradus does not take part in the infernal sacrament: he points out the right instrument and directs the carving.
All this is as it should be; the world needs Gradus. But Gradus should not kill kings. Vinogradus should never, never provoke God. Leningradus should not aim his peashooter at people even in dreams, because if he does, a pair of colossally thick, abnormally hairy arms will hug him from behind and squeeze, squeeze, squeeze. (note to Line 171)
It seems that VN never revisted his home city (renamed Leningrad in 1924), because he was aware of the pun: "Nabokov is persona lennon grata."