More than six decades after it was written, a short handwritten note that helped assemble one of rock's most famous line-ups is heading to auction. The letter was sent by guitarist Brian Jones to drummer Charlie Watts in June 1962, before the group had even settled on its name, and it has stayed with the Watts family ever since, only now coming to light through the late drummer's sister.

Jones wrote to Watts at his childhood home in Wembley, opening with an apology for the forwardness of his approach and asking where the drummer stood with Alexis Korner's Blues Incorporated, the band Watts was then playing with. He had noticed another drummer filling in at a show in Ealing the previous night, and he wanted to know whether Watts might be free to play rhythm and blues with his own group instead. The pitch was confident to the point of cheek: Jones described his band as already tightly knit and better than Korner's outfit, and said the group rehearsed three days a week.

The note also gives a snapshot of the band before fame, listing a line-up of two guitars, harmonica, piano and drums, with a bass guitar still to come, and closing with a joke at the expense of the drummer then in the chair. Sotheby's music specialist Craig Inciardi has described the document as an unusually direct record of the band's formation, written weeks before its first performance and months before Watts formally joined.

Watts went on to anchor the band's sound for nearly six decades, and the letter is now the centrepiece of Sotheby's New York Rock and Pop sale on December 15, with an estimate of $70,000 to $80,000. That figure reflects its place in the group's origin story rather than any musical content: this is a recruitment note, not a song, and its value lies in the moment it captures.

For collectors, the appeal is the combination of rarity and provenance. The letter has never been offered before, it comes directly from the drummer's family, and it documents a decision that shaped popular music.