Blake Lively knows that sisterhood lasts forever.

The Gossip Girl alum posted an adoring tribute for her former Sisterhood of the Traveling Pants costar America Ferrera after attending a Barbie event.

"Some weeks are for the man in your life. Some weeks are for the women," the A Simple Favor actress wrote in an Instagram post on Dec. 17. "I was so happy to celebrate my denim sister @americaferrera. She's the heart and soul of @barbiethemovie because she's the heart and soul of everything she's a part of."

Blake—who, along with Sisterhood stars Alexis Bledel and Amber Tamblyn, supported America at the SAG-AFTRA Foundation panel on Dec. 15 in New York City—went on to gush over her former costar's Barbie performance.

"That speech she gives as Gloria felt as close to real as anything I've ever seen on screen. Because that's who she is. She's that spectacular, passionate, inspiring and full of heart in her own life," the Age of Adaline star added. "I've known her for 20 years. Since I was 16. I've watched her live, grow, soar, fall, make, break, push, fight, win, create, forge, disrupt, way make, lead, lead, lead."

The It Ends With Us star packed on the support for her sister. "I can't wait to watch her sweep awards up across her living room floor. No one deserves it more… for a lifetime of brilliant work," she continued. "It's one of my life's honors to witness her show so many women not only what's possible, but HOW it's done. I love you sister. Always."

And, of course, Blake couldn't resist preaching the thesis of the actress' 2005 film. 

"Pants = Love," she topped off the post. "Love your sisters. Love yourself."

America responded to her sister's post in the comments. 

"When your girl gives good hype," the Ugly Betty star replied, adding some heart emojis. "I love you forever sis."

The Sisterhood meetup on Dec. 15 marks the first time the cast has made a public appearance since 2017—when the stars supported Amber at her directorial debut for the Paint it Black premiere in New York City. 

And while fans are hopeful another sequel for the iconic film series is in the works, Amber has said another movie would be "very complicated," given the former stars' schedules and family obligations. 

Either way, it's clear America, Amber, Alexis and Blake continue to support each other and pass the pants. Read on for more Sisterhood highlights from the SAG-AFTRA Foundation event. 

Blake Lively, Amber Tamblyn, America Ferrera and Alexis Bledel, stars of the 2005 movie Sisterhood of the Traveling Pants, reunited Dec. 15, 2023 at a SAG-AFTRA Foundation panel event for Barbie, which featured Ferrera, one of the film's stars, as a speaker. She later shared videos of their reunion.

The girls pose for pics at the event, as seen in videos shared by Ferrera.

The actresses pose for a selfie.

"The Sisterhood came through all in pink to celebrate my performance in Barbie last night," Ferrera wrote on Instagram. "I love these women with all my heart. #SisterhoodForever."

Lively embraces Ferrera.