London, UK - More than half a century after the Beatles split up, a new single by the legendary British band was released Thursday featuring all four members.

John Lennon originally wrote the song Now And Then in the late 1970s at his home in New York's Dakota Building. The song was one of several tracks on a cassette Lennon recorded for Paul McCartney, a year before Lennon's tragic death in 1980 at age 40.

The last two living band members McCartney (81) and Ringo Starr (83) were only just able to release the song with a little help from innovative AI software developed by Peter Jackson of Lord of the Rings fame.

Recording at Capitol Studios in Los Angeles, they managed to isolate Lennon's vocals and add more backing vocals, as well as Starr's drum part alongside bass, piano, and a slide guitar solo by McCartney that was inspired by Harrison.

Starr noted that the process "was the closest we'll ever come to having him [Lennon] back in the room so it was very emotional for all of us."

"It was like John was there, you know. It's far out," he said.

"It's a genuine Beatles recording," McCartney added, saying it is the "final" song from the Fab Four.

Now And Then is being released as a double A-side, with the band's 1962 debut single Love Me Do and cover art by artist Ed Ruscha.

The track was unveiled by Apple Corps, Capitol, and Universal Music Enterprises with a music video directed by Peter Jackson due to debut on Friday.