EXCLUSIVE: Reese Witherspoon Dishes on 'Mindy Project' Guest Spot & Daughter Ava's Upcoming 18th Birthday

The actress opened up to ET about being 'in shock' over her daughter upcoming milestone.

Reese Witherspoon is headed to The Mindy Project, and she couldn't be more excited to be a part of the acclaimed series.

The Oscar winner stopped to talk with ET's Cameron Mathison at the Los Angeles premiere of her new film, Home Again, on Tuesday, where she dished on her involvement in the celebrated sitcom.

"I did a little cameo on Mindy, we'll see what happens. It was really fun," Witherspoon shared. "Mindy's a great dear friend of mine for many years, so I was happy to be there in her last season."

The news of Witherspoon's cameo in the Hulu comedy series was revealed by Kaling herself in an snapshot she shared to Instagram on Tuesday morning. The side-by-side pics showed the stars hanging out in a cave as part of the episode.

"Our latest #themindyproject guest star is the only woman i would want to be trapped in a cave with. (This is weirdly the second cave we have acted in together!)" Kaling wrote in the caption.

Witherspoon and Kaling also star together in Ava DuVernay's hotly anticipated fantasy epic A Wrinkle in Time, alongside Oprah Winfrey. The actresses play a trio of celestial beings.

In her upcoming romantic comedy Home Again, Witherspoon stars as a single mom whose life is turned upside down when she allows three young men, who are aspiring filmmakers, to move into her house, where she also lives with her kids. Things really get complicated when her estranged husband (Michael Sheen) returns to live with her.

The movie is the directorial debut of Hallie Meyers-Shyer -- daughter of legendary rom-com creator Nancy Meyers, who worked alongside her daughter as a producer on the project.

"They were a great team!" Witherspoon shared. "I've never worked with a mother-daughter team before, so this was really a first for me and it was really fun and nice to see those family dynamics."

"[They're] such a nice family. They've come up in this business together and it's nice to see them [working together]," she added.

Witherspoon's own super sweet family dynamic with her daughter, Ava Phillippe, was also on display on Tuesday, as the lookalike pair walked the carpet together at the premiere.

Frederick M. Brown/Getty Images

As her little girl is about to turn 18 on Sept. 9, the actress says the milestone has left her "in shock."

"I alternate between crying and feeling really proud of the woman she's become," she joked. "She's my best friend and we do everything together, it's going to be hard for her to leave! But I have another year!"