McDonald's announces 'Grandma McFlurry': But what's in it?

McDonald's is being deliberately vague about the ingredients of its new Grandma McFlurry, but the internet already has theories.

(WJW/NEXSTAR) – McDonald’s is releasing a new McFlurry said to be inspired by — and celebrating — grandmas.

On Thursday, McDonald's announced its new “Grandma McFlurry,” to be available for a limited time starting May 21.

The new McFlurry is made with vanilla soft serve blended with "delicious syrup" and chopped pieces of candy, according to a McDonald's press release.

When contacted, however, a representative for McDonald's would not specify the flavor of the syrup or the candy, only saying it tastes "reminiscent of grandma's favorite treat that she hid in her purse."

Even still, several curious fans on social media have already theorized that butterscotch will be among the flavors in the Grandma McFlurry, with one user — who claimed to be an employee — alleging that a shipment of "butterscotch crumble" was delivered to the restaurant where they work.

As of Thursday, there were no ingredients or allergen information available for the Grandma McFlurry on the official McDonald's website. A representative for McDonald's said customers "will have to try it" to find out the flavors for themselves.

"The Grandma McFlurry tastes like a trip down memory lane, and we're excited to give our fans that experience while honoring the grandma figure in all our lives," Tariq Hassan, the chief marketing and customer experience officer at McDonald's, said in a statement included with the release.

Ahead of the Grandma McFlurry's debut, McDonald's will be rolling out the "Grandma's McFlurry Mobile" in New York City, giving out free samples in Herald Square on May 17 before visiting a series of assisted-living facilities in East Harlem and Queens on May 18.

McDonald’s says the new McFlurry is available while supplies last.