London, UK - Paul McCartney has expressed his gratitude after the Beatles legend was reunited with a missing bass guitar that he owned in the 1960s and used on several Fab Four tracks.

McCartney played the original Höfner bass throughout the Beatlemania decade, including at Hamburg's Top Ten Club, at the Cavern Club in Liverpool, and on early Beatles recordings at London's Abbey Road studios.

It was used to record hits including Love Me Do, She Loves You, and Twist and Shout.

The instrument was then thought to have been lost during the London Get Back/Let It Be recording sessions in January 1969, but an investigation last year discovered that it was actually stolen in 1972.

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The investigation was led by a guitar expert and two journalists, who launched a fresh drive to reunite the guitar with McCartney, vowing to solve what they branded "the greatest mystery in rock and roll."

After receiving hundreds of leads and suggestions, the "Lost Bass Project" pinpointed when and where it was stolen and other information before eventually discovering its most recent whereabouts.

"Following the launch of last year's Lost Bass project, Paul's 1961 Hofner 500/1 bass guitar, which was stolen in 1972, has been returned," a post on McCartney's official website stated.

"The guitar has been authenticated by Höfner and Paul is incredibly grateful to all those involved."

The "Lost Bass Project" said it was "thrilled."

"Despite many telling us that it was lost forever or destroyed, we persisted until it was back where it belonged," the search team said on its dedicated website.

McCartney bought the left-handed Höfner 500/1 Violin Bass for around £30 – about £550 ($585) today – in Hamburg in 1961, during The Beatles' four-month residency at the Top Ten Club.

Its appearance became unique after being overhauled in 1964, including with a complete respray in a three-part dark sunburst polyurethane finish, with McCartney maintaining it as a back-up bass.

The search team say it learned that the guitar had been stolen in 1972 from a van in London's Notting Hill neighborhood and was then given to a local pub landlord.

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Eventually, it ended up in the attic of a terraced house in the south coast of England, with the homeowner only realizing that the prized instrument was there following last year's publicity.

The original thief "didn't set out to steal the Beatles' bass and he didn't know he was taking such a piece of Beatlemania history," Scott Jones, one of the trio involved in the hunt, told BBC radio.

"It was too hot to handle and that's when he decided to give the bass up to his local pub."

Jones' wife Naomi added: "The amazing thing is we thought when we started this search, that it could have been anywhere in the world."

She noted there are big Beatles collectors in Japan and the team had tips that it could be in a millionaire's house in Jamaica.

"Actually the geography of all of this is just a few miles in and around Notting Hill."