Michael Fassbender, an actor from Prometheus, has been talking about the film and in an interview with MTV he says Prometheus is still an Alien film:
“Oh, absolutely. There’s a definite connecting vein,. You realize you’re part of something else, but it’s definitely in keeping with the old ones.” … “When I read it, I was like, ‘Well, okay, another Alien. Where do you go with this idea?’ And then I sort of read the script, and it’s new, yet it’s in keeping with the old traditions as well. But there’s a whole new revelation within this film.”
Thanks to Slashfilms, dandan and Darkoo.