Dr Greer claims the truth is so top-secret that sub groups within government would not even confirm it to the president.
He goes one step further and alleges it is a military-industrialist cabal of semi-public/semi-private interests and has access to technology reverse-engineered from alleged crashed UFOs.
Dr Steven Greer makes an outlandish claim in his documentary unacknowledged
So how does Dr Greer justify such outlandish claims?
He added: “Look, we stampeded into Iraq after 9/11 without there being a scintilla of evidence that Iraq had anything to do with 9/11 and we know now that that was completely a hoax.
“The majority of people already believe there is intelligent life out there and the last poll I saw said that 43 percent of Americans think we’re currently being visited.
“More than half the public all over the world believes that UFOs are real and that governments are hiding something. So that battle has been won, but the larger argument has to still be engaged.”
Dr Greer spoke to the paper about his new film Unacknowledged: An Exposé of the Greatest Secret in Human History, ahead of its Toronto premier.
Looking at the alleged cover up over the years, it is directed by Michael Mazzola and narrated by Breaking Bad’s Giancarlo Esposito.
Dr Greer got $700,000 (£543,000) through crowd funding to make it happen, and it looks at his work with The Disclosure Project, set up to try to lift an alleged “truth embargo” on the existence of aliens.
He said: “And that’s why we made this film, in part, to expose what the secret agenda has been and the disinformation campaigns.”