Mary-Kate and Ashley Snuff Out John Oliver's 'Olsen Twins Conspiracy'

Mary-Kate and Ashley Olsen appeared TOGETHER in NYC ... ending the conspiracy that they are actually just one girl moving back and forth really quickly.

The very private 31-year-old ex "Full House" stars were seen together having a smoke break.

John Oliver recently discussed the theory on his HBO show, "Last Week Tonight."

It was a good conspiracy theory while it lasted, but we guess it's back to discussing how NASA faked the moon landing.

!youtube-embed(https://www.youtube.com/watch?v=pyra-0rJRXk)