The 48-year-old actor, who is also a guitarist worked on the track after helping the singer record her initial vocal idea, reported Contactmusic.
"It's all Johnny Depp. He's a friend of mine and I got the idea for the song in my head. I told Johnny, 'I don't wanna forget this.' So he recorded me singing a capella. Then Johnny said he would send it to me so I wouldn't forget," Smith said.
"And when I got it, he'd put drums, guitars, everything on it! So the first minute of the song is all me and Johnny Depp. What we did in the recording studio was the band listened to Johnny's track and then came in on the chorus," she added.
Another track on the album pays tribute to Amy Winehouse, who died of accidental alcohol poisoning last year.