The guitar on which Sir Paul McCartney learned his first chords has sold for £330,000 at an auction at London's Abbey Road Studios.
The guitar comes with a letter of authenticity from Sir Paul
The instrument, which fetched more than three times its estimate, was sold by Sir Paul's school friend Ian James, who will use the money for his retirement.
The Rex acoustic guitar helped Sir Paul persuade John Lennon to let him join his band, The Quarrymen, in 1957.
He impressed Lennon by playing songs and chords on it at a Liverpool fete.
Sir Paul has provided a letter of authenticity that will be given to American buyer Craig Jackson, a spokesman for the Cooper Owen's Music Legends auction said.
"The above guitar, belonging to my old school pal Ian James, was the first guitar I ever held," Sir Paul wrote.
"It was also the guitar on which I learned my first chords in his house at 43 Elswich Street, Liverpool 8."
Sir Paul remembered Mr James, a father-of-three from Ormskirk, Lancashire, in a Beatles biography written by Hunter Davies.
A photo of Sir Paul with the guitar was included in the sale
At the fete, he showed Lennon "a few more chords he didn't know", he told the author.
"Ian James had taught me them, really. Then I left. I felt I'd made a good impression, shown them how good I was."
The guitar Lennon was playing on the day - an acoustic Gallotone Champion - was auctioned for £155,500 in 1999.
In 2004, a Gibson SG guitar played by George Harrison and Lennon sold for £294,000 at auction in New York.
The Rex guitar also features in two photographs included in the sale.
In one, Sir Paul is seen playing the guitar in his office earlier this year.
The other was taken by Sir Paul 49 years ago, showing a young Mr James with the instrument.
The guitar's buyer, Mr Jackson, himself the president of an auction company, said: "This is such an important piece of rock history and I am an extremely happy man tonight.
"Without this guitar The Beatles may never have existed and it is a fantastic acquisition."