Blake Lively Went Brunette for a Spooky 'Sisterhood of the Traveling Pants' Reunion With Amber Tamblyn

In the spirit of both tricks and treats, Sisterhood of the Traveling Pants alumni Blake Lively and Amber Tamblyn surprised followers with a Halloween reunion.

On Sunday, Tamblyn shared a video of herself opening a package from Lively's newly launched line of non-alcoholic mixers, Betty Buzz.

"This was the biggest package I've ever received in the mail," Tamblyn said as she opened a red box filled with five small bottles of various mixers. "There was like a whole package," she continued, panning the camera up to her face, "and then there was like a person inside of the package, it was really weird," she said, allowing the camera to reveal an unmistakably Blake Lively-like figure standing behind her in a brown wig and a red sequined blanket.

"@BettyBuzz really has outdone itself on marketing by sending me this gorgeous box of tasty refreshments and a life-size Blake Lively Halloween mannequin for my front yard," Tamblyn joked in the post's caption. "#HappyHalloween #SisterhoodNerds4Ever."

It's hard to believe it's been 16 years since Lively, Tamblyn, Alexis Bledel, and America Ferrera first brought Ann Brashares's Y.A. touchstone to the silver screen.

Ferrera celebrated the anniversary this past June with a shoutout to the fictional pair of pants that would come to bond her and her co-stars, as well as a loving ode to the crew's "questionable fashion choices."

"Why am I orange? Where is Amber's crimp & curl now? Was anyone's hair color natural? 2000's, you were messy, but magical," she captioned a throwback image of the foursome.