"Launching the first two Doritos Locos Tacos were obvious," Taco Bell President Brian Niccol said in a statement announcing the new flavor. "Nacho Cheese is the top-selling Doritos flavor and our fans asked us for Cool Ranch. For the third DLT, we heard our customers as they told us they wanted something spicy and with flavor."
A Taco Bell spokesperson said the Fiery flavor will be exclusive to the chain, however "it is closest to Flamas, which is available in select regions in the U.S."
A Doritos spokeswoman confirmed the Fiery flavor is nearly identical to its Flamas chips, which have been available at least since 2011. "The new Fiery Doritos Locos Taco product mirrors the flavors fans enjoy from Doritos Flamas flavored tortilla chips. Based on customer feedback during testing, a few changes were made to create Fiery Doritos Locos Tacos including the use of a red shell, and a more descriptive name," she told CNBC via email late Wednesday.
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"People palettes' have really evolved, people are looking for a lot of spice," said chef Richard Sandoval who runs 37 restaurants such as Maya in New York and is featured on the current season "Top Chef Masters" on Bravo. "I've seen it in my own restaurants. Ten years ago, people weren't looking for heat."
Bravo is owned NBCUniversal, which also owns CNBC and CNBC.com.
Sandoval, whose restaurants are far more upscale than Taco Bell, is nonetheless a fan of the concept, he said. Sandoval consulted with the restaurant years ago, but is not affiliated with the current launch.
"I think Mexican has evolved in the last 10 to 15 years immensely and they've just leapt on that."
"It's brilliant what they did," by reinventing themselves with the Doritos shells on one end of the menu and more authentic Mexican food on the other, he said.
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The new Taco Bell tacos will sell for $1.39 each and $1.69 for a supreme size. The regular will contain 170 calories and 10 grams of total fat; the supreme will have 200 calories and 12 grams of total fat, according to the company.
Taco Bell is owned by Louisville, Ky.-based Yum Brands., which owns Pizza Hut and KFC. Doritos is owned by Purchase, N.Y.-based PepsiCo.
—By CNBC's Amy Langfield. Follow her on Twitter @AmyLangfield.
This story was updated from its original version to add comment from a Doritos spokesperson.