In fact, the story comes immediately after Jesus tells a number of parables that all begin with the same kind of language:
“A certain man had a fig tree….” (The parable of the barren fig tree, Luke 13:6)
“A certain man gave a great supper….” (The parable of the great supper, Luke 14:16)
“A certain man had two sons….” (The parable of the prodigal son, Luke 15:11)
"There was a certain rich man….” (The parable of the unjust steward, Luke 16:1)
The parable of the rich man and Lazarus begins the same way: