The Beatles will release one final song, 'Now and Then.' How did it come together?

It's a moment more than 40 years in the making.

The Beatles, who officially split up in 1970, surprised the world Thursday morning by announcing one final song, "Now and Then."

The song, which was written and sung by John Lennon in the late 1970s and developed by Paul McCartney, George Harrison and Ringo Starr in the 1990s, has finally been finished by McCartney and Starr decades later, according to a news release.

"Paul called me up and said he wanted to work on 'Now and Then,'" Starr said in the announcement video. "He put the bass on, I put the drums on."

Strictly speaking, "Now and Then" should be an impossibility. Lennon — one half of the band's core songwriting partnership, with bassist McCartney — was murdered in 1980. Guitarist Harrison died of cancer in 2001. Only McCartney, 81, and drummer Starr, 83, remain.

So where did "Now and Then" come from? How can it really be "the last Beatles song?"

Your questions, answered.

Who wrote "Now and Then?"

Lennon — at least in its original guise. In 1975, he retreated from the music scene to raise his newborn son, Sean. But he never stopped writing and demoing songs at his home in New York City's Dakota Building. While many of Lennon's final compositions eventually appeared — in polished studio form — on his 1980 comeback album with wife Yoko Ono, Double Fantasy, and their posthumous 1984 collection Milk and Honey, a handful remained in Ono's vault. "Now and Then," recorded at Lennon's piano in 1979, was one of them.

How did it become a Beatles song?

On January 19, 1994 — some time after Harrison and longtime Beatles' sidekick Neil Aspinall reportedly pitched Ono on the idea of fleshing out Lennon's unreleased demos with full-band instrumentation and vocals — Ono gave McCartney two cassette tapes.

One featured "Free as a Bird" and "Real Love," two late Lennon demos that the surviving Beatles (aka The Threetles) ultimately "finished off" during 1994 and 1995 reunion sessions at McCartney's home studio in Sussex, England and released as part of the sprawling 1995-1996 Beatles Anthology project.

"It's the end of the line, really," Starr said at the time. "There's nothing more we can do as the Beatles."

But that wasn't entirely accurate. Ono also turned over a second tape — allegedly labeled "For Paul" — with two additional Lennon demos. "Grow Old with Me" had already appeared on Milk and Honey, so McCartney, Harrison and Starr set it aside. But "Now and Then" was new and together they spent two days in March 1995 recording a rough backing track.

Why didn't the Beatles release "Now and Then" earlier?

Harrison lost interest.

Like the original "Free as a Bird" and "Real Love" tapes, "Now and Then" had some imperfections. For the other two reunion songs, producer Jeff Lynne and his team used existing 1990s technology to iron out problems with pitch, timing and tape noise. But "Now and Then" was a more embryonic composition — "The song had a chorus," Lynne explained, "but is almost totally lacking in verses" — so Harrison apparently concluded that completing it wasn't worth all the effort.

"George just didn't want to rework it because it's not a matter of putting some vocals, or a bit of bass and drums to finish it," an unnamed participant in the sessions told the Daily Express in 2007. "With this, you have to really build the song."

In a 2012 interview, McCartney was more blunt. "George went off it," he said, launching into an imitation of his occasionally ornery former bandmate. "'Ugh. F***ing hell. F***ing rubbish, this.' It’s like, 'No George, this is John!' 'This is f***ing rubbish, you know.' 'Oh, OK then.'"

McCartney then vowed to "nick in with Jeff and do it — finish it — one of these days."

Why are the Beatles releasing 'Now and Then' now?

Because McCartney kept his word — with a little help from his friend Ringo — and ultimately both the Harrison and Lennon estates signed off.

In June, McCartney told the BBC that he had "just finished" what he described as "the final Beatles record," adding that he had extracted Lennon's voice from an old, unnamed demo using artificial intelligence.

A few months later, in September, Starr told the Associated Press that while he and McCartney had recorded new parts during secret 2022 sessions — including drums, vocals and a McCartney guitar solo — Harrison's original 1995 rhythm guitar tracks have been preserved, making "Now and Then" the "last track ever that you'll get the four Beatles on."

More details were unveiled in Thursday's announcement, including a "wistful, quintessentially Beatles string arrangement" and "backing vocals from the original recordings of 'Here, There And Everywhere,' 'Eleanor Rigby' and 'Because.'"

"Besides John's vocal, 'Now And Then' includes electric and acoustic guitar recorded in 1995 by George, Ringo’s new drum part, and bass, guitar and piano from Paul, which matches John’s original playing. Paul added a slide guitar solo inspired by George; he and Ringo also contributed backing vocals to the chorus," the news release said.

What does artificial intelligence have to do with it?

Fans freaked out when McCartney mentioned AI, presumably because they imagined a fake robot Lennon that had been generated from existing audio data and programmed to "sing."

But McCartney was referring to a different kind of technology — in this case, the same machine-assisted learning program developed by director Peter Jackson's team and recently used on other Beatles’ projects to isolate, clarify and remix individual voices and instruments.

"[Jackson] was able to extricate John's voice from a ropey little bit of cassette. We had John's voice and a piano and he could separate them with AI. They tell the machine: 'That's the voice. This is a guitar. Lose the guitar,'" McCartney told BBC's Radio 4 Today program in June. "So when we came to make what will be the last Beatles record, it was a demo that John had that we worked on … We were able to take John's voice and get it pure through this AI so that then we can mix the record, as you would normally do."

As a result, Lennon's voice sounds much sharper on "Now and Then" compared to "Free as a Bird" or "Real Love" — but it’s still Lennon.

What are the Beatles saying about it?

"There it was, John's voice, crystal clear," McCartney said in Thursday's announcement. "It's quite emotional. And we all play on it, it's a genuine Beatles recording. In 2023 to still be working on Beatles music, and about to release a new song the public haven't heard, I think it's an exciting thing."

"It was the closest we’ll ever come to having him back in the room, so it was very emotional for all of us," said Starr. "It was like John was there, you know. It’s far out."

"It was incredibly touching to hear them working together after all the years that Dad had been gone," Sean Lennon said. "It’s the last song my dad, Paul, George and Ringo got to make together. It’s like a time capsule and all feels very meant to be."

The track will be released on Nov. 2 with original cover art by renowned artist Ed Ruscha. A 12-minute Now And Then – The Last Beatles Song documentary will debut on Nov. 1, and a music video will drop on Nov. 3.