Duffy has shared a second new song since revealing she withdrew from the public eye after being raped, drugged and held captive for weeks.
The Welsh singer-songwriter, 35, said the track, titled River In The Sky, was “for better days to come” as she shared it on her Instagram page.
The mournful ballad features a chorus in which Duffy sings “Why, why do we cry?” over a piano accompaniment.
In one verse, she sings: “I walk this life/Doubt on my mind/I pray to fly, burden free/She covers me so patiently/As I learn to deal with the pain.”
Duffy, whose full name is Aimee Anne Duffy, debuted a song called Something Beautiful on BBC Radio 2 in March, weeks after breaking her silence.
Aside from a contribution to the Legend film soundtrack in 2015, she had not released new music since her second studio album, Endlessly, in 2010.
In April she posted a lengthy statement online, revealing that she was “raped, drugged and held captive”, and had spent years recovering from the ordeal.
She wrote: “Of course I survived. The recovery took time. There’s no light way to say it.
“But I can tell you in the last decade, the thousands and thousands of days I committed to wanting to feel the sunshine in my heart again, the sun does now shine.
“You wonder why I did not choose to use my voice to express my pain? I did not want to show the world the sadness in my eyes.
“I asked myself, how can I sing from the heart if it is broken? And slowly it unbroke.”