Musician/artist Moby is a somber dude ... particularly when a famous actress calls him out for lying! Natalie Portman says Moby's claim in his new book "Then It Fell Apart" that the two dated in 1999 is completely false. SO EMBARRASSING!

Now Moby's cancelled his book tour, apologized a couple times on Instagram and said he's going to "go away for a while." Well he's still here! And we asked him what's up ...