The release of producer Michael Bay's Teenage Mutant Ninja Turtles big-screen reboot has already been announced for December 2013.

But while you might expect fans to be happy with the news there will soon be more Turtles films to watch, more Turtles toys to buy and more Turtles-branded fast food to scarf, it turns out the fans are actually furious.

(And yes, there really are still hardcore Turtles in the world.)

So why are the fans so hot and bothered in their half-shells? Because the Transformers director has announced that the Turtles will be aliens in the new film, not mutants.

Speaking at a Nickleodeon event at the Jazz at Lincoln Center in New York, Bay said: "When you see this movie, kids will believe one day that these turtles do exist, when we're done with this movie.

"These turtles are from an alien race, and they're going to be tough, edgy, funny and completely loveable."

Michael Bay talks Teenage Mutant Ninja Turtles by stuffwelike

Aliens? Until now the Turtles were regular Earth turtles mutated into humanoids by green goo, which is what gave them their powers. For those who weren't nine years old in 1992, those powers basically comprise martial arts, the ability to make wisecracks and an obsession with pizza.

In any case, messing with one of the four words in Teenage Mutant Ninja Turtles hasn't gone down well.

"I think Bay has long since abandoned his ability to feel shame," said Katey Rich at Cinema Blend.

Others were even more upset:

@Meli_Molina
Melissa Molina

*Reads news on new Teenage Mutant Ninja Turtles movie* *Hits head against table repeatedly*

March 19, 2012 4:11 pm via web Reply Retweet Favorite

@clink_movies
Naomi Creason

Michael Bay intent on ruining my childhood. Ninja Turtles are aliens in his reboot. http://t.co/jJ65PaeZ

March 19, 2012 1:29 pm via web Reply Retweet Favorite

@DudeWabiSabi
Lamenzo

They want to ruin my beloved TMNT. Piss off Michael Bay! Piss right off!

March 19, 2012 2:58 pm via Twitter for iPad Reply Retweet Favorite

But for some the disappointment was hardly a surprise. Stu Heritage at the Guardian wrote: "The last 20 years have ensured that expectations of any new Teenage Mutant Ninja Turtles movie couldn't possibly be any lower," he said.

"And yet, thanks to a combination of Bay, (director Jonathan) Liebesman and a deliberately misunderstood origins story, it looks like we might all end up being disappointed anyway."

The movie ('Ninja Turtles') will released on 25 December 2012.