Nocturnal Animals co-stars Isla Fisher and Amy Adams know that you can't tell them apart, but they're not the least bit offended.

"I find it a huge compliment because I think Amy's gorgeous," Fisher told ET's Carly Steel during a recent sit-down.

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Adams admitted that even she can see the resemblance at times.

"Sometimes I've been like, 'Oh yeah! I can totally see it,'" Adams said. "But she's small and cute, and I'm sort of not as small or as cute," she joked.

While Fisher doesn't mind the confusion, she revealed that it can sometimes lead to awkward situations.

"I've been mistaken for her a couple times in my career. One of them was kind of amazing because it was Lady Gaga. She congratulated me for my performance in American Hustle."

Adams received an Oscar nomination for her role in the 2013 crime drama.

Fisher said she was too embarrassed to correct Gaga, so she just politely accepted the pop singer's compliment and "slunk away."

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"I'm a big fan of Amy," Fisher gushed. "I think she's an extraordinary performer, particularly her performance in this is just really brilliant."

In the film, Adams stars as the ex-wife of a novelist (Jake Gyllenhaal), whose violent book is interpreted as a veiled threat against her.

According to director Tom Ford, there was no coincidence involved in the casting of the female leads.

"It's very important to the story that these characters resemble each other," Ford said. "I was absolutely struck by the similarities of their appearance, but also by their ability to act."

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While this marks Adams and Fisher's first film together, they have been friends for years. They first met while auditioning for the same role in the 2002 biopic Catch Me If You Can. The part ultimately went to Adams.

"Amy and I are both girls' girls, and we're both very friendly, so we just started chatting," Fisher said about meeting Adams at the audition. "I remember around the time she was in Junebug and she was nominated for an Oscar. I just remember it was so exciting, because she was like my peer and we'd started out together and it gave me hope that maybe I'd last more than a minute in the business."

Not only are they good friends, they're around the same age (Adams is 42, while Fisher is 40) and they're both moms. Fisher told ET that their daughters are in the same dance class.

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With all this in common, the two actresses were relaxed around each other on set, but going to work with Ford might have added a little stress to their jobs.

Fisher admitted that she usually puts wardrobe on at the last minute after hair and makeup, but switched up her routine in order to impress the famous designer.

"I didn't want Tom to wander in the makeup trailer and see my regular clothes," she said.

Adams assured us that fans will not be disappointed by the clothes in the film.

"I did wear some Tom Ford, just not exclusively," said Adams. "But I was still styled by him, make no mistake. There were details."

Nocturnal Animals hits theaters Nov. 18.