Reese Witherspoon Confesses She Was 'Terrified' On The Set Of 'Friends': 'My Brain Was Somewhere Else'

Reese Witherspoon popped up a few times on Friends — she played Rachel Green's sister — but she confessed it wasn't all rainbows and butterflies.

"I was terrified. I was out of my body…. My body was there and then my head and my brain was somewhere else. I'd just had a baby," she shared while appearing on Late Night With Seth Meyers.

"The funny storyline was that I started dating Ross because she and Ross were ‘on a break,'" she said, referring to how her character, Jill Green, falls for Ross (played by David Schwimmer). "And [Rachel] was – gets really jealous and she's like ‘You can’t date Ross.' And I was like ‘I can’t? The only thing I can't have is dairy."

"I still remember the line," she quipped. "Their writing was so good on that show, so it's really memorable … I have all sorts of funny, famous Friends lines that are stuck in my head. Don't y'all?"

The show, which ran from 1994 to 2004, was widely successful, and the Legally Blonde star, 46, recalled Jennifer Aniston making her feel welcome while filming the sitcom.

"I was terrified, but Aniston was so sweet to me. She was like, ‘They don’t care if you mess up. They actually like it better when you mess up,'" the blonde beauty said.

Witherspoon also recalled what it was like what she first walked into the famous coffee shop.

"Walking into Central Perk, that main coffee place, and sitting on the couch, I was like ‘Oh my God, I can’t believe this is happening. Oh my God, there's Joey. Oh my God,'" she stated.

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As OK! previously reported, Witherspoon and Aniston, 53, currently star in The Morning Show.

The mom-of-three previously gushed over her pal and how they immediately connected.

"I was really nervous, and she was like, ‘Oh, my gosh, don't worry about it!' I marveled at her ability to perform in front of a live audience like that with no nerves. They would change all the lines and she was just so effortlessly affable, bubbly, and sunny. We've been friends ever since," she said.