Belles de Jour

The fourth season premiere showed cameos from prominent members of the fashion and film industry. During the Fashion's Night Out party, fashion models Corinna Drengk and Karlie Kloss make a cameo appearance as Lily's guests and French actress and fashion model Lou Doillon makes a cameo during Serena and Blair's double date.[7] A new love interest for Blair had been cast for the Paris story arc. French actor Hugo Becker was cast as Louis Grimaldi, a member of the Monégasque royal family and suitor to Blair.[8]

Although credited, Taylor Momsen (Jenny Humphrey) does not appear in this episode.[9] When discussing Momsen's return to filming in the show, producer and Gossip Girl writer Stephanie Savage stated, "We want to keep it up in the air where her character will go" and hoped to create tension with her absence, also stating that Momsen would return for an episode for the first half of the season. 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.[10]

Michael Ausiello of Entertainment Weekly stated that a new love interest for Nate would be cast, confirming rumors that Nate and Serena's relationship has ended.[11] Former Melrose Place star Katie Cassidy joined the cast as Juliet, a student at Columbia University and a potential love interest for Nate, with an agenda against Serena, together with David Call as Ben Donovan, Juliet's imprisoned brother.[12][13]

News spread that a new love interest for Chuck would be cast. 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.[15][16]

Blake Lively filming in Saint-Germain-des-Prés, Paris, France.

Various news medias announced the fourth season premiere of Gossip Girl would be filmed in Paris. EW's Tim Stack revealed that the show would be filming two episodes in the French capital, anticipated whether it could rival the same Parisian trip that Sex and the City had done years prior and jokingly requested that show stylist Eric Daman dress Leighton Meester in a gown to equal Sarah Jessica Parker's multi-lyered Versace outfit.[17] Archana Ram revealed the new clothes that the show's character would be wearing for the Paris story arc.[18] French magazine Grazia revealed that the show would be shooting at the French University, La Sorbonne in the Latin District (or Quartier Latin) of Paris on July 5, with Clémence Poésy joining the cast in the same filming location.[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. Stephanie Savage stated that Vogue's Fashion's Night Out would be incorporated into the story arc.[10] Leighton Meester and Blake Lively filmed the double date scene at the French restaurant Bacarat.[7]

While filming, Blake Lively commented on the show's fashion for the premiere and her experience of dressing up in Paris. "I feel like just in general, people here dress a little more fabulous [with] things that are a little more old glamor. It's a little bit more glamorous in Paris. You can get away with it." Meester also praised the elevation of the fashions usually seen in the show. "The wardrobe in this show is incredible, but in Paris it's been over-the-top amazing. They just really have taken it to the next level...because we're in Paris and because Blair is starting a new life."[21]

The opening montage features Leighton Meester wearing a printed Moschino frock with Blake Lively dressed in a Georges Chakra couture dress and a Haute Hippie ruffled emerald green wrap dress.[22][23][24] Lively was later seen wearing Suno pink palazzo pants while Meester appeared in a pink Oscar de la Renta frock.[25] Meester also wore a Maxime Simoëns dress.[26]