Popeyes' chicken sandwich was such a massive success it helped the chain crush the competition even after it sold out

Sandwich buzz bumped sales across the menu.

"We sold more bone-in chicken, which has been our flagship product for so many decades," Athayde said. "We sold more tenders, we sold sides, we sold drinks, we sold dessert."

Even in the two weeks when the chicken sandwich was on the menu, Athayde said, fewer than half of orders included the sandwich.

"I think we just want to continue telling our fans how amazing our food is — not only the sandwich, but all the rest of our menus," Athayde said.

"We saw more people have started to notice the brand and started to try it and realize how amazing the food that we serve is," Athayde continued. "I think that's our job moving forward, to continue that momentum."

More people downloaded Popeyes' app.

When Popeyes ran out of the chicken sandwich, customers were instructed to download the Popeyes app to be alerted when the sandwich returned to menus. On Monday, at 7:15 a.m. ET, everyone with a Popeyes app received a push notification that the sandwich would return on Sunday.

Bruno Cardinali, Popeyes' head of marketing for North America, declined to share exactly how many people downloaded the app, but said that there was a "good, interesting spike in downloads" after the chicken sandwich sold out.

"When we pushed the notification at 7:15 a.m. Eastern Time, we saw immediately a lot of people basically posting on Twitter and other social media channels a screenshot of their phones — just to be the first one to tell everyone the sandwich is coming back on November 3rd," Cardinali said.

New customers swarmed to Popeyes.

Restaurant Brands International said in a call with investors on Monday that one of Popeyes' biggest missions is to get new customers to try the brand. While executives said that Popeyes' chicken sandwich typically beats most rivals in taste tests, only about 65% of the US has eaten at the chain.

The chicken sandwich helped Popeyes draw in new customers in the last quarter. According to Athayde, the sandwich both convinced regulars to visit more frequently and attracted people who hadn't eaten at Popeyes before.

"They were attracted by the buzz — they tasted it, they liked it," Athayde said. "We attracted a whole new business towards our brand. And, I think it's gonna help elevate the brand for many, many years to come."