James Cameron's return to Pandora is going to take longer than he expected.

According to The Associated Press, the filmmaker revealed he's delayed production of the three Avatar sequels after writing the screenplays proved to be a complex undertaking. The first sequel in now targeted for release in late 2017, a year later than planned, with the subsequent two films arriving in 2018 and 2019.

All three films will be shot simultaneously, which is where much of the complexity has arisen; Cameron now hopes to have the scripts finished by the end of this month.

"We're writing three simultaneously. And we've done that so that everything tracks throughout the three films," the director said while in Wellington, New Zealand. "We're not just going to do one and then make up another one and another one after that.  "And parallel with that, we're doing all the design. So we've designed all the creatures and the environments."

Released in 2009 by Fox, Avatar is the highest-grossing film of all time, with a box-office haul of $2.8 billion.