A composition by Coldplay frontman Chris Martin recorded when he was just 12 is up for sale after being discovered by a schoolmate.
The cassette features the star - then a pupil at Exeter Cathedral School - on the keyboard.
His three-minute track, which he composed and called Electric Thunder, won a music competition at the school.
Simon Corser, now 40, who is selling the tape, also entered the 1989 competition but lost to his schoolmate.
He told the PA news agency that fellow pupils had been "really amazed" at this composition.
The track was "quite original" and "does show signs of real talent," he said.
Corser, from Chorley, Lancashire, said that it was "not only well played but original. We didn't have a chance!
The whole school were humming it after he played it. You'd walk down the corridor and people were humming it.It was quite good and very catchy."
She had bought the recording of the musical production, which was being sold to raise money for the school, because her son's flute performance was also on it.
The cassette is now estimated to fetch up to £600 at Omega Auctions of Merseyside.
I completely forgot about him for many years," Corser, who is not a pop music fan, said.
Corser said he also remembers Martin winning a public speaking competition - when he gave an address on How To Learn To Ride A Unicycle.
"I remember him saying, 'When you're steadying yourself, make sure you're not holding on to your mother's favourite bit of furniture," Corser said.
Coldplay fans later saw the star riding a unicycle, dressed as an elephant, in the video for the track Paradise.
Auctioneer Paul Fairweather said he believed the tape "is almost certainly Chris Martin's first published recording".
"Whilst it's no Yellow," he said in reference to the hit Coldplay track, "we think the composition has plenty about it!"
Omega Auctions of Merseyside will sell the tape on February 25 with an estimate of £400 to £600.