The Biggest Lie Colin Firth and Emma Stone Tell Their Co-Stars

PHOTO: Colin Firth and Emma Stone on "Good Morning America," on July 16, 2014.PlayABC
WATCH Colin Firth, Emma Stone on Working With Woody Allen

Colin Firth and Emma Stone's new movie "Magic in the Moonlight" is based on many themes, one being that a white lie can be good if it helps the greater good.

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Stone, 25, and Firth, 53, both admitted during an interview with ABC News that they are no stranger to telling a little fib if it avoids hurting someone's feelings.

"Have you ever gone backstage after a friend of yours' performance that's really bad?" Firth asked Stone during a group conversation.

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With a huff and a sigh, Stone relented and said, "Yeah."

The "Amazing Spider-Man" actress admitted that she's definitely lied and said "great job" when maybe the compliment wasn't warranted.

"Yeah I have, that's a good point," she fired back at Firth. "Or like, 'OMG, you looked beautiful,' that's my favorite compliment. ... 'You looked great!'"

Firth, an Oscar winner, added that he has one line he uses often -- "You must be exhausted."

Stone joked that you can also ask "Aren't you tired? ... There's so many!"

The two stars of Woody Allen's latest film about magic also took a crack at predicting one another's future.

"I think it's going to fall apart quite quickly for Emma," Firth joked about where Stone would be in five years. "But, I'm no expert, I could be wrong."

"Colin, please stop saying this to everyone," Stone replied. "It's all over for me."

"Magic in the Moonlight" hits theaters on July 25.