The letter was expected to go for somewhere between $30K and $50K -- but there was a flurry of bidders at the end of the 17-day online auction, pushing the final price up early Saturday morning for auction house, Gotta Have Rock and Roll.
As for the purchaser's identity ... they're opting to remain anonymous for now.
As we reported ... Lennon signed the letter -- which is the last known legal doc with his autograph -- before sending it to his accountant, Barry Nichols. It listed the names of 3 proxies Lennon chose to vote at an annual meeting for the Beatles corporation, which was to be held 9 days later in London.
Hours after writing it, Lennon was fatally shot by Mark David Chapman outside The Dakota, John and Yoko Ono's NYC apartment building. Chapman was convicted in 1981 for the murder and sentenced to life in prison.