The pair have recorded a track for the new Coen brothers film 'Inside Llewyn Davis', which stars Timberlake and Mumford's wife Carey Mulligan, reported Ace Showbiz.
"OK I can tell you this. There's a Coen brothers film coming out soon that I was lucky enough to work with Oscar Isaac and Carey Mulligan," Timberlake said.
"And coincidentally I did work with Marcus Mumford on the soundtrack, so I became very good friends with them. Marcus and myself, we all kind of worked on the music together and I don't know any other world where we would have the opportunity to collaborate like that but it was so much fun.
'Inside Llewyn Davis' is expected to be released in cinemas later this year.