A letter from John Lennon to Eric Clapton in which the former Beatle promised he could take Clapton to new musical highs if they worked together is hitting the auction block. The hand-written letter will go on sale at the Profiles in History auction in Los Angeles on Dec. 18, according to Reuters. Auctioneers expect the document to fetch somewhere around $30,000.

The Beatles had broken up by the time Lennon, who was shot to death at age 40 in 1980, wrote the letter to Clapton on Sept. 29, 1971. He proposed the two start a new band together.

“Eric, I know I can bring out something great, in fact greater in you that had been so far evident in your music. I hope to bring out the same kind of greatness in all of us, which I know will happen if/when we get together,” Lennon wrote.

The letter was drafted about three weeks after “Imagine,” Lennon’s most popular single as a solo artist, was released, according to a CBS timeline of the singer’s life.

Clapton had long been associated with the Beatles by this point in rock history. When lead guitarist George Harrison briefly threatened to quit the Fab Four in 1968, the other three group members were prepared to replace him with Clapton in the event Harrison didn’t return. He collaborated with the band on “While My Guitar Gently Weeps” and with Lennon’s Plastic Ono Band.

Auctioneer Joe Maddalena told Reuters the circumstances in each musician’s career makes the letter that much more significant.

“There was a point in time when George Harrison thought about leaving the band and his replacement was Clapton, so this letter is a link of what could have been,” Maddalena said.

Clapton later would write “Layla” about his unrequited love for Harrison’s then-wife, Patti Boyd. The song appeared on Clapton’s Derek and the Dominoes album and would go on to become one of the most beloved songs of the era.

In October of 2012 a book of letters Lennon wrote throughout his life went on sale, allowing fans to get a peek into the singer’s psyche. Vulture reported that Lennon was as cranky as he was talented, writing scathing letters to groupies, critics and especially fellow former Beatle Paul McCartney.

“I’m not ashamed of the Beatles - I did start it all - but of some of the s*** we took to make them so big. I thought we all felt that way in varying degrees,” Lennon wrote in one. “Do you really think most of today’s art came about because of the Beatles? I don’t believe you’re that insane, Paul.”