Titled Last Goodbye, it is an emotional ballad that failed to make a place to the former Disney star's latest album Bangerz, reported Ace Showbiz.
In the break-up anthem, Cyrus, 21, talks about a dying relationship.
"We never said that we would be perfect/ We only said that we tried/ And when you said that we were forever/ I guess that's just another lie," she sings.
A snippet for Last Goodbye leaked last year. Fans then speculated that the song was about the singer's then-fiance, Liam Hemsworth.
Last Goodbye is the second Cyrus song that leaked in the past few days. Previously, the demo version of a party jam called 'Pretty Girls (Fun)' landed online.