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The 32-year-old mama-to-be looked every bit the fashionista in a Mary Katrantzou floral dress which perfectly hid her bun in the oven.
The Hart of Dixie star paired the look with Bionda Castana white pumps with black ankle straps.
Bilson chatted with E!'s own Kristin Dos Santos during the event and gushed about working on the upcoming season of her hit show.
"I guess I felt pretty good because we have a solid thing going at this point and we have so many fun things to play with and it's so different from any other show on the network," she explained.