Disney's D23 EXPO 2017After scoring an Emmy nomination for her role in HBO miniseries "Big Little Lies," Reese Witherspoon is returning to the small screen. Only this time, she's trading dark comedy for a straight-up sitcom.

Witherspoon has booked a secretive appearance on the upcoming sixth and final season of "The Mindy Project," with star Mindy Kaling revealing the cameo in a post on Instagram.

"Our latest #themindyproject guest star is the only woman i would want to [be] trapped in a cave with," Kaling captioned the snap, which features a shot of her character, Mindy Lahiri, clad in a puffy vest and clutching her phone, apparently gazing at Witherspoon, who's all smiles and sporting a cute red dress. The actress also revealed their puzzling location, adding in an aside, "This is weirdly the second cave we have acted in together!"

Kaling is likely referring to the stars' roles in the upcoming adaptation of children's fantasy novel "A Wrinkle in Time," in which they play Mrs. Who (Kaling) and Mrs. Whatsit (Witherspoon), two of three magical beings who shepherd a young girl on an intergalactic journey to find her missing father. (The third member of that trio is Mrs. Which, played by none other than Oprah Winfrey.)

Based on Kaling's photo, we're guessing Witherspoon's "Mindy" appearance will be some sort of dream sequence. Kaling's character has referenced the Oscar winner before on the show, famously crafting what she dubbed a "Wreath Witherspoon" holiday decoration that spawned real-life internet imitators.

Witherspoon isn't stopping her small screen renaissance anytime soon: After "Mindy," she's set to work with Jennifer Aniston (with whom she once starred on "Friends," playing Rachel's younger sister in a short guest arc) on a series about a morning talk show. That project is currently being shopped to networks and streaming services.

Keep your eyes peeled for Witherspoon's cameo when season six of "The Mindy Project" hits Hulu on September 12.

[via: Mindy Kaling/Instagram]