Sometimes even the most famous celebrities still get star struck by their coworkers. That was the case when Jennifer Aniston was cast alongside Julia Roberts in Gary Marshall's forthcoming ensemble film, "Mother's Day."

On Wednesday night, Aniston walked the red carpet at the premiere of the film at the famous TLC Chinese Theatre in Hollywood, Calif., where she discussed working with Roberts and how intimidated she was by her during some of their scenes together.

"It's just a different thing when you get to work with them and then you're doing what you both do, [but] together," Aniston said. "I even flubbed in the first take and called her Julia!"

Aniston was also asked why she was at all "intimidated" by working with the Academy Award-winning actress.

"Because it's Julia Roberts! Oh my gosh," she responded.

Aniston and Roberts had been friends for decades, and Roberts even guest starred in an episode of "Friends" in 1996 prior to their starring in "Mother's Day" together. Aniston said that being friends with someone you respect and actually working with them were two completely different things.

While Aniston was freaking out about working with Roberts, someone else had the same feeling about working with Aniston herself - "Pretty Little Liars" star Shay Mitchell. At the premiere of "Mother's Day," Mitchell got candid about what it was like working alongside Aniston.

"She is so wonderful," the actress said. "She truly made me feel so comfortable from the moment I got in, because I was kind of like, 'Hi?!' But you can't show that, and she was so wonderful and so amazing to work with."

Aniston may have accidentally called Roberts by her real name during one of their scenes together, but Mitchell said she was trying not to call Aniston by her "Friends" character name.

"I was just scared that I would say, 'Rachel!' " she joked. "The whole time I was like, 'Shh, shh.' "

"Mother's Day" follows in the footsteps of Marshall's other films "Valentine's Day" and "New Year's Eve." This is also the fourth time Roberts and Marshall have teamed up for a film together after "Pretty Woman," "Runaway Bride" and "Valentine's Day."

"Mother's Day" hits theatres on April 29 and also stars Kate Hudson and Jason Sudeikis.