The third "Ghostbusters" installment is happening - just not with Ivan Reitman at the helm.

The "Ghostbusters 1-2" director says he's officially turned down the opportunity to direct the long-awaited follow-up, which he says will likely begin production in early 2015 with an all-new cast of spook-hunters.

“I wasn’t sure what I was going to do, and it was never clear what Bill [Murray] was going to do,” said Reitman in an exclusive interview with Deadline. “A lot of things happened in the last few months, the most significant of which was the passing of Harold [Ramis], who was a very good friend who was extraordinarily influential in my career. We did five movies together including both 'Ghostbusters.'”

As to the question of the ever-elusive Murray, Reitman said actor became "literally impossible" to track down when they pursued him for the original version of the threequel written by Lee Eisenberg and Gene Stupnitsky ("The Office," "Bad Teacher"), saying: “It was a really good script, but then it became clear that Bill really didn’t want to do another 'Ghostbusters'...When Bill finally…well, he never actually said no, but he never said yes, so there was no way to make that film."

The version that's actually being made now is less a sequel than an out-and-out reboot scripted by Etan Cohen ("Men in Black 3," "Tropic Thunder"), in which an all-new team of Ghostbusters will be introduced and the original cast will play only a "very minor role."

Sadly for fans, of course, Ramis is no longer around to participate, and the actor/writer/director's death seems to have been a major factor in Reitman's decision to hand the reins over to another filmmaker. “With Harold no longer with us I couldn’t see it," he said.

So how many Ghostbusters will there be in this new installment? For his part Reitman isn't telling, but he says fans of the first two films have no cause to worry.

“We are determined to retain the spirit of the original film, and I am pleased that all of this seems to have happened organically,” he said. “I’m hoping we can get started by the fall, set in New York, but given the logistics and the stuff that happens, the beginning of 2015 seems more likely.”

How do you feel about this new version of "Ghostbusters"? Let us know in the comments.