The story of how Michael Jackson ruined a friendship but saved Sesame Street in the process.

One of the reasons why Sesame Street has remained on the air for more than 40 years is because it appeals both to young children and the parents who watch it with them. And because producers know parents are watching, the show features guest appearances from stars that kids wouldn’t know but adults would, like Tina Fey or Jon Hamm, and educational songs that are parodies of well-known pop songs. In the ‘70s, for example, “Bruce Stringbean and the S. Street Band” performed “Born to Add,” a parody of Bruce Springsteen’s “Born to Run.”

One of the most famous Sesame Street parodies ever: “Letter B,” a spelling-centric parody of the Beatles’ “Let It Be,” as performed in 1983 by a group of Muppet musicians with mop-top haircuts called “The Beetles.”

Under a copyright law called “Fair Use,” parodies may be recorded and released without securing permission from the song’s copyright owner. At the time “Let It Be” was controlled by a music publishing company called Northern Songs. In 1981, ex-Beatle Paul McCartney, along with Yoko Ono, widow of ex-Beatle John Lennon, attempted to buy Northern Songs, so McCartney and Lennon’s family could own the Beatles songbook. The deal fell through.

A couple years later, McCartney collaborated with Michael Jackson on the hit “Say, Say, Say.” Jackson had just made a ton of money from the success of his Thriller album and asked McCartney for financial advice. McCartney told him to invest in music publishing. Jackson did—in 1985, he purchased Northern Songs, and bought McCartney’s songs out from under him.

Jackson inherited one other thing from Northern Songs: a nasty lawsuit. Northern Songs was in the process of suing Children’s Television Workshop for $5.5 million. Reason: copyright infringement over “Letter B.” CTW is a nonprofit group, and a payout of that magnitude likely would have crippled the company and led to the end of Sesame Street, a beloved TV show around the world, and credited with helping millions of children learn to read.

While the purchase of the Beatles’ catalog permanently soured Jackson’s friendship with McCartney (they never collaborated or even spoke again), Jackson at least did one nice thing—immediately after the deal finalized in 1985, he cancelled the lawsuit. Children’s Television Workshop paid $50 to settle the case, which “Letter B” songwriter Christopher Cerf paid himself.