Pink Floyd’s David Gilmour auctioned off his guitar collection for $21.5 million Thursday in a record-setting event at Christie’s. Among the axes sold: an iconic Fender used on “The Dark Side of the Moon.”

The “Black Strat,” a 1969 Fender Stratocaster that Gilmour subsequently modified, was sold for $3,975,000 to Indianapolis Colts owner Jim Irsay. The sum was the most ever paid for a guitar at auction, according to Christie’s.

Irsay also snapped up a C.F. Martin six-string acoustic that figured in the Pink Floyd tracks “Wish You Were Here” and “Shine On You Crazy Diamond.”

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The 73-year-old songwriter said he’ll donate the proceeds of the 127-lot sale to ClientEarth, a London-based environmental group.

The previous record for an auctioned guitar was $2.7 million for a Fender Stratocaster signed by 19 musicians including Sting, Paul McCartney, Eric Clapton and Jimmy Page to raise money after the 2004 Asian tsunami.