Blake Lively and Amber Tamblyn Have Mini Sisterhood of the Traveling Pants Reunion on Halloween

Blake Lively and Amber Tamblyn had a mini Sisterhood of the Traveling Pants reunion for Halloween.

The Gossip Girl alum, 34, made a silly cameo in a video Tamblyn, 38, posted Sunday to Instagram. "Look what I got in the mail!" the Y: The Last Man actress said while unboxing a gift from Lively's drink mixer brand Betty Buzz.

"Ooh, Betty Buzz! It's so beautiful," Tamblyn continued. "Look inside, it's so pretty! So, this was the biggest package I've ever received in the mail. There was like a whole package, and then there was a person inside of the package. It was really weird."

She panned the camera up to reveal Lively standing over her shoulder, sporting a brunette wig with a red sequined cloth draped over her head.

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Warner Brothers/Courtesy Everett Collection Cast of The Sisterhood of the Traveling Pants

"@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 captioned the post.

The pair starred alongside America Ferrera and Alexis Bledel in 2005's The Sisterhood of the Traveling Pants and the 2008 sequel, based on the young adult novels by Ann Brashares. The cast celebrated the movie's 16th anniversary in June.

Lively previously opened up to PEOPLE about the bond she still shares with her costars. "America Ferrara, Amber Tamblyn, Alexis Bledel – those are three women who I met when I was 16 years old and I've been lucky to call them my friends and mentors ever since," she said.

"What they do – whether artistically, politically, socially, personally – they really use their voice, and whether people agree with their voice or not is not the thing that I'm most concerned with as much as, it's nice to see women who are not only empowering themselves but empowering other women to stand up and to really fight and work for what they believe in," Lively added.