Every Gossip Girl episode title is a word play on the title of a movie. This episode's refers to Belle de Jour (1967).
Was filmed in Paris.
Starting from this episode, Taylor Momsen is mostly conspicuously absent. Jenny was sent away to Hudson, and her future appearances will unfortunately be limited due to the actress pursuing her career as a rock star with her band.
The original idea was that Blair (Leighton Meester) would push Serena (Blake Lively) into the Seine, but the producers realized that would seem too hostile, and fortunately opted for the fountain instead.
Clémence Poésy (Eva Coupeau) ends up playing the wife of Tom Hiddleston in The Essex Serpent (2022), playing Stella Ransome and Will Ransome respectively. Sebastian Stan (Carter Baizen), who appears in several earlier episodes of the show, has worked with Tom in the Marvel Cinematic Universe, a group of movies based on the Marvel Comic Books. They play Bucky Barnes/Winter Soldier and Loki respectively.