When "X-Men" director Bryan Singer needed a second opinion on "X-Men: Days of Future Past," he turned to one of the authorities in science-fiction movies: James Cameron.

Singer's "Days of Future Past" features a similar time-traveling, edge of the Apocalypse story line to Cameron's iconic "Terminator" films.

So who better to turn to for advice on a time-travelling movie than Cameron himself?

According to Comingsoon.net, Singer sent Cameron an early cut of "Days of Future Past" for review and the "Terminator" director had a suggestion for the tone of the film's original ending.

For those who don't remember, in "Days of Future Past" Wolverine is sent into the past to prevent a destructive future in which mutants are nearly destroyed by giant Sentinels. At the end of the film, we see Wolverine successfully alter the past and return to discover a new timeline.

"When Wolverine is walking around [in the final scene] he’s seeing things in kind of a blurriness," Singer told Comingsoon. "So I sent that to Jim and Jim called me up and goes ‘Bryan, that blurry thing made me think that the wool was going to be pulled out from under me and I was not satisfied. I thought it was going to be a lie and it had failed and it would all be dark, and then suddenly it was okay.’"

Singer said Cameron enjoyed the film but thought the original ending implied the team's last ditch effort to prevent mutant extinction had failed. It may have felt more like a dream sequence that wasn't real.

"... He [Cameron] said ‘Let the audience enjoy the fact that it all turned out okay… in that future,'" said Singer. "So I pulled the effect off and my editor was like ‘Oh I like it, it’s so cool and weird!’ and I’m like ‘Shut up, it’s coming off!’”

While Cameron enjoyed the film, Singer did add the director was disappointed by one other thing.

Apparently, the cut of the film Singer sent Cameron's way didn't include the secret cameos that came as a surprise to viewers. At the film's end, Famke Janssen, James Marsden, and Anna Paquin reprise their roles as Jean Grey, Cyclops, and Rogue from the original 2000 film.

“I explained that to Jim and I said ‘By the way, it didn't have these three cameos’ and he goes “OH Why didn’t you tell me that? That makes a big difference dude in letting me enjoy the ending of the g---amn f---ing movie!" added Singer.

The next film in the X-Men series, "X-Men: Apocalypse," is coming May 27, 2016.