Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
According to Ada (the title character of a novel, 1969, by VN), the servants called Ben Wright (the English coachman in “Ardis the First” who is associated with farts) “Bengal Ben:”
Nonchalantly, Van went back to the willows and said:
‘Every shot in the book has been snapped in 1884, except this one. I never rowed you down Ladore River in early spring. Nice to note you have not lost your wonderful ability to blush.’