(NEXSTAR) – McDonald’s founder Ray Kroc didn’t exactly have high hopes for the Filet-O-Fish sandwich.

In fact, he was betting against it.

In the early 1960s, McDonald’s only offered a handful of items, including hamburgers, cheeseburgers, fries, milkshakes, soft drinks, coffee and milk. This presented a problem for McDonald’s franchisee Lou Groen, whose clientele in Cincinnati largely abstained from eating meat on Fridays.

“That area was 87% Catholic,” Groen once explained to the Cincinnati Enquirer. “On Fridays we only took in about $75 a day.” 

Inspired by the sales of a competitor’s fish sandwich, Groen decided to develop his own, made with fried halibut and tartar sauce. But first, he had to get it OK’ed by the suits at McDonald’s, many of whom had reservations because of its “more complicated cooking process,” according to the chain.

Ray Kroc was among the skeptics. Plus, he already had plans for his own meat-free “Hula Burger,” consisting of a slice of grilled pineapple and cheese. (He also believed that McDonald’s restaurants would be “stunk up with the smell of fish” as a result of Groen’s idea, Groen once told the Cincinnati Business Courier.)

Lucky for Groen, Kroc was willing to try both ideas and let the sales speak for themselves.

“Ray said to me, ‘Well, Lou, I’m going to put your fish sandwich on (the menu) for a Friday. But I’m going to put my special sandwich on, too. Whichever sells the most, that’s the one we’ll go with,’” Goren told the Cincinnati Enquirer.

Kroc also made a “side bet” with Fred Turner, another McDonald’s executive, that the Hula Burger would sell better than the Filet-O-Fish — the stakes being a brand-new suit.

On the day of the test, Groen’s restaurant sold 350 fish sandwiches and only six Hula Burgers. So not only was Kroc wrong about the Filet-O-Fish, but he now owed his colleague a new suit.

Kroc wasn’t too bummed, of course, because “McDonald’s got the Filet-O-Fish,” according to McDonald’s historian Mike Bullington.

After a little bit of tweaking (e.g., halibut was swapped for Atlantic cod, a slice of cheese was added), the new McDonald’s fish sandwich began to be embraced by franchisees across the country. In 1965, it was added to the restaurant’s permanent nationwide offerings, becoming the first new addition to the original McDonald’s menu.

Groen, meanwhile, enjoyed continued success as a McDonald’s franchisee into the 1980s, operating dozens of restaurants in Ohio and Kentucky. He passed in 2011, but remained a fan of the Filet-O-Fish throughout his final years — but he still preferred his original version to the sandwich that ended up on the nationwide menu.

“My halibut sandwich far outshines that one,” he remarked to the Cincinnati Enquirer in 2007.