After news broke that Friends" fans couldn't help but reminisce about the first time the pair worked together: When Witherspoon guest-starred as Aniston's sister on the hit NBC sitcom. And it seems like Witherspoon is also feeling nostalgic about that first collaboration, based on the way she chose to wish her once and future co-star a happy birthday.

Aniston celebrated her 49th birthday on February 11, and among the flood of well wishes from famous friends and fans alike, one message in particular stood out.

"Happy Birthday to my work sister #JenniferAniston !!" Witherspoon wrote on her social media accounts, accompanied by a photo from one of the two "Friends" episodes she appeared in as Jill Greene, Rachel's baby sister.

In the scene pictured, Rachel is introducing Jill to the rest of the gang, when Joey (Matt LeBlanc) throws out his signature "How you doin'?" pickup line. A protective Rachel quickly shuts him down, though later, she does orchestrate a date between Jill and her ex, Ross (David Schwimmer). Naturally, awkward shenanigans ensue.

So far, we don't know too much about Witherspoon and Aninston's new series, though it's based in part on a book that chronicles the drama behind the scenes of morning news shows. Fingers crossed that they'll find a way to reference the actresses' shared "Friends" past in some way.

[via: Reese Witherspoon/Instagram]