Animorphs authors Katherine Applegate and Michael Grant reveal they have exited the upcoming movie adaptation. From 1996 to 2001, married couple Applegate and Grant wrote the Animorphs series under the name K. A. Applegate. Geared towards kids, the series was comprised of 54 books in its main run, with ten companion novels being released over the years as well. Animorphs followed five human kids - Jake, Marco, Cassie, Rachel and Tobias - who gain the ability to transform into any animal they touch. With the aid of alien Aximili-Esgarrouth-Isthill (nicknamed Ax), the Animorphs battle a secret alien infiltration of Earth.

Despite having a dedicated fanbase, there has yet to be a feature film adaptation of Animorphs. A television show ran for two seasons in the late 90s, but aside from that, fans have waited many years for a big screen venture. An Animorphs film first inched toward development in 2015, but it wasn't until June of this year that it made real progress. Scholastic and Picturestart announced their intention to develop an Animorphs movie, thrilling fans. However, it has now run into a pretty big obstacle.

Related: New Animorphs Graphic Novel Coming This October

Grant took to social media on Tuesday to announce he and Applegate have decided to step away from the Animorphs film adaptation. "With great sadness we have decided not to participate further in the

@picturestart effort," Grant wrote. He didn't elaborate further, aside from the fact that their exit is due to creative differences. Grant also said they might talk about it more in the future, but for now, he'll only direct them to a piece written by Percy Jackson author Rick Riordan.

The Riordan piece is a post from his blog, wherein he discusses his experiences with watching his books get turned into movies. The Percy Jackson films are widely regarded as poor adaptations by fans, and Riordan has been outspoken about his displeasure with them. In the post Grant shared, Riordan specifically highlights emails he sent to the producers where he discussed issues with the script, such as the aging up of the main characters and the pointless plot alterations. Since Grant shared Riordan's post while discussing his own departure from the Animorphs film, it seems likely that he and Applegate were facing the same issues as Riordan.

This will surely come as a disappointment for fans who were looking forward to Applegate and Grant having a hand in the Animorphs movie. Fans typically feel more excited about an adaptation if the original creators are involved, and when the creators leave over something like creative differences, they understandably get nervous (See: what happened with Netflix's Avatar: The Last Airbender series). There's still a chance Animorphs will turn out alright, but there's a bit more cause for concern now.

More: Animorphs Deserves A New Video Game Adaptation With Next-Gen Graphics

Source: Michael Grant/Twitter