A guitar donated to a charity auction by Pink Floyd guitarist David Gilmour sold at Christie’s this summer for an astounding $3.975 million. The 1969 Fender Stratocaster set the record for a guitar sale; estimates had only put the final bid in the $100K-$150K range.

The piece of rock-n-roll history was made several years after Leo Fender sold his company to CBS. Without its rock-legend associations, the guitar would be valued at between $15K and $20K. The gavel price speaks volumes about perceived value of such instruments, and of the increasingly mythological dimensions of the rock renaissance that occurred during the era of the late 1960s and early 1970s, when blues forms and psychedelic experimentation merged into pop-culture relevancy.

The Black Strat was Gilmour’s main instrument throughout the heyday of Pink Floyd, and afterward. The sound of the guitar provided the mournful, searching blue-note tones on ‘Dark Side of the Moon’ and other studio albums, and was used by the musician on numerous tours.

At the same auction, two other guitars owned for decades by Gilmour also outpaced their estimates. A 1954 Stratocaster in white and gold, known by its ‘0001’ serial number, sold for $1.815 million. A 1969 Martin dreadnought acoustic, which was used to record numerous Pink Floyd classics, including the hit ‘Wish You Were Here’, sold for $1.095 million.

The auction raised $21.5 million for ClientEarth, a trailblazing environmental justice NGO.