[6] The fourth season premiere opens with Serena van der Woodsen (Blake Lively) and Blair Waldorf (Leighton Meester) spending their vacation in Paris to move on from their troubles.

Vanessa Abrams (Jessica Szohr) returns to New York and finds Dan Humphrey (Penn Badgley) living with Georgina Sparks (Michelle Trachtenberg) and a baby, while Nate Archibald (Chace Crawford) attempts to move on from his breakup with Serena, he befriends Juliet Sharp (Katie Cassidy), a girl with ulterior motives for helping him.

Meanwhile, back in New York, Eleanor helps make arrangements for the Fashion's Night Out gathering at the Van Der Woodsen apartment and Dan and Nate prepare to face Serena.

Savage also dispelled rumors that Italo-French songwriter and wife to the President of France, Carla Bruni, would make a guest appearance nor would famous director and producer Woody Allen.

Producers started casting the recurring role of Eva, an utterly gorgeous female in her 20s or 30s who boasts a warm heart and an authentic French accent.

[14] Hollywood and media business blog, The Wrap announced that Harry Potter actress Clémence Poésy had been cast as Eva and would be a part of a four episode story arc.

[19][20] Joe Adalian and Diane Gordon of New York Magazine revealed more filming locations from Musée d'Orsay, the Eiffel Tower, Gare du Nord to Avenue Montaigne.

"Chuck’s survival and new life are set up to be the episode’s big shocker, but I was taken by a different revelation: After Blair decided for the umpteenth time that she was tired of living in Serena’s shadow, it dawned on me that the Serena-Blair relationship is the great, central romance of Gossip Girl.

The “will they break it off?” tension between the two characters has informed plenty of plots and multi-episode arcs in the series’ past, but “Belles du Jour” truly let that relationship breathe as it built momentum toward the next episode.

It also paid off in one of the show’s best punch lines in a long time, as Blair’s bitchy, entitled nature boiled to the surface and plunged Serena into a fountain.

"[32] The closing montage featured Juliet with photos and visual cross references on the Upper East siders, leading fans to speculate if she was Gossip Girl.

An interview with the New York Post dispelled rumors when Katie Cassidy jokingly stated that she was not portraying Gossip Girl but understood how the episode had been set up to make fans assume.