Lady Gaga and Justin Bieber are aliens in 'Men in Black 3'

You may have suspected that Lady Gaga and Justin Bieber are not of this world. Now there's proof.

OK -- "proof" may be a bit strong. But the two pop stars will be among the faces on the alien surveillance board in "Men in Black 3," which continues the series' tradition of celebrities making cameos as extraterrestrials.

Star Will Smith hinted at Gaga's cameo at an international junket in February, and "MIB3" director Barry Sonnenfeld confirms it, along with appearances by Bieber and filmmaker Tim Burton, in an interview with Collider.

"One of the joys is deciding who you would put up on the board, who you would tell the world are aliens," Sonnenfeld tells the site. "And A) the challenge is you have to get permission from these celebrities and B) you don't want to go with people that are either a flash in the pan, or political, or people that in 10 years no one will know who you're talking about."

Gaga and Bieber join a list of "Men in Black" celebrity aliens that includes Steven Spielberg, Sylvester Stallone, Martha Stewart and Danny DeVito. Michael Jackson also did a brief appearance in "Men in Black II" as a would-be agent.