She does apparently have a good reason for this switch though, writing in her Instagram caption: "When your husband asks you to 'go blonde' for a role... you say yes."
Currently, Brie is in pre-production for the film The Rental, which is her husband Dave Franco's directorial debut and centres around two couples who rent a vacation home but — plot twist — everything goes wrong. And for that role, Franco envisioned Brie as a blonde.
This is the biggest hair change we've seen for the actress, who's stuck with brunette hair for the entirety of her career and only played with highlights occasionally. But with that wavy bob and golden hair colour, Brie is now entirely on trend for summer '19.