A lost recording of a duet by Sir Mick Jagger and Carly Simon has reportedly been unearthed after 45 years.

Rolling Stones record collector Matt Lee claims to have found the tape of the track, which is believed to have been recorded in 1972, around the same time it was rumoured Simon's hit song 'You're So Vain' was about the 'Satisfaction' group's 75-year-old frontman.

Though she denied he was the subject of the track, Jagger is believed to have contributed uncredited backing vocals on the song.

According to The Daily Telegraph, Matt said he sent it to Rolling Stone magazine in hope they would pass the recording onto Simon.

He said: ''I'm not doing it for the money.

''I'm a collector. My motive for sending it to Rolling Stone was to pass it to Carly.''

The lost track is believed to be called 'Fragile', and was performed with the pair sat singing at a piano.

Jagger is said to sing lead vocals, with Simon adding harmonies.

Simon, 73, previously revealed that the tape had gone missing and sung part of the lyrics in an interview in 2016.

She said: ''We had this little back and forth at the piano for about an hour.''

She belted: ''Funny, funny, funny, funny, funny, How love can make you cry.''

The track isn't completley new to fans, as in the 1972 documentary on the Stones' tour of America, Jagger can be heard singing, ''It's funny, funny, funny'', in one scene.

Then the song was known by the name 'Schoolboy Blues', a nod to the film entitled 'Cocksucker Blues'.