Finish the detective's thrilling novel about a spectacularly clumsy cat burglar. Choose the correct words to fill the gap.

Little _____ that the "priceless diamond" he just stole was actually a shiny piece of plastic from a board game.

The correct answer is did he know.

In this context, the word "Little" acts as a negative adverb meaning "almost not at all." When a sentence starts with "Little" for stylistic emphasis, we must invert the subject and the auxiliary verb. For the past simple tense, we add the auxiliary "did" to get "did he know."