It's still not listed on IMDb, but the most recent newsletter from Sophie Kinsella seems to confirm it:
... the Shopaholic movie is finally underway! I have been in New York recently, attending rehearsals, talking to the actors, director and producers, and seeing the story come alive before my eyes... and it's given me goosebumps :) Isla Fisher, Hugh Dancy and Krysten Ritter are going to be SO fabulous as Becky, Luke and Suze.
Surely Sophie knows who's playing Luke?
Related posts: More Shopaholic casting news | First photo of Shopaholic movie


