An uncovered John Lennon letter reveals the bitter breakup of The Beatles

The Beatles' breakup in 1970 left some bad feelings both in the band and among its followers, but a newly uncovered letter written by John Lennon exposes just how poisonous things got.

The undated typed letter, with handwritten annotations, is being auctioned off by RR Auction at an estimated value of $20,000 or more.

In the letter, which was likely sent around 1971, Lennon addresses his ex-bandmate Paul McCartney and McCartney's wife Linda, in an apparent reply to correspondence from Linda.

Lennon tells her, "I was reading your letter and wondering what middle aged cranky Beatle fan wrote it."

Lennon also reacts to negativity surrounding his relationship with Yoko Ono at the time, which continues to be a sore spot for Beatles fandom - with some fans even alleging that Ono was somehow responsible for the Beatles breakup.

"I hope you realise what s--- you and the rest of my 'kind and unselfish' friends laid on Yoko and me, since we've been together," Lennon wrote.

Lennon goes on to say that he doesn't "resent" Paul McCartney but instead feels "sorry for him."

Curiously enough, however, he does say "love to you both" at the end, in spite of all the acrimony.

If you've ever wondered what was swirling around the breakup of one of the greatest bands of all time, it's an essential, albeit nasty, read.

See images of the letter below: