When James Corden premiered his “Carpool Karaoke” segment featuring Paul McCartney on his CBS Late Late Show in June, it was much longer than usual – and much more emotional. Tonight at 8 ET, in a prime-time special, it’s even longer…

Their televised trip down memory lane, and Penny Lane, was unveiled during a special London week visit by The Late Late Show. Corden, as usual with his beloved “Carpool Karaoke” segments, picked up his celebrity passenger and drove around as they sang to a mixtape of that person’s greatest hits and other assorted songs. What was less usual was the location (McCartney’s home town of Liverpool), the segment’s length (23 minutes of screen time), and the amount of time spent stepping away from the vehicle.

Before it was over, this “Carpool” took McCartney down Penny Lane, to his childhood home, and to a neighborhood pub where he and his future Beatles bandmates once performed. With his current band, as a surprise to that day’s patrons, McCartney staged an impromptu mini-concert and performed again.

The week the lengthy “Carpool” segment with McCartney was televised by CBS, seen by about 1 million viewers, the network released it on YouTube, where it went viral immediately. As of today, it’s generated 30 million views – and tonight, CBS presents a one-hour prime-time special, Carpool Karaoke: When McCartney Met Corden Live from Liverpool, promising some unused footage from that memorably sweet and emotionally resonant feature.

(Days after the original feature first aired, I reviewed it, in glowing terms, on NPR’s Fresh Air with Terry Gross.)

The segment managed to be nostalgic yet current, playful yet deeply moving. McCartney visited his childhood home, now run as a visiting attraction by the National Trust, for the first time since he moved away, and visited the barber shop written about in his “Penny Lane.” He and Corden sang along to McCartney songs old and new while driving around Liverpool, and performed more of the same at the Philharmonic Pub.

Brian Ray, the guitarist in McCartney’s band on records and in concerts since 2002, told me in a phone interview last night that the unannounced Liverpool concert was an amazing thing to witness, much less to be on stage performing with McCartney.

“It’s just incredible to be able to be in a privileged position of standing beside Paul, who’s experiencing again, all these years later, the places that he frequented, that really informed who he was and formed who he was,” Ray said.

“The Philharmonic Pub is a pub they went to go hang out and have a beer at, and yes, they did play out here. So there are just memories locked in there that will never leave, because the place hasn’t changed one bit. It’s a proper pub.”

One of my favorite moments occurs when Corden, standing behind the bar, pours a beer for McCartney, who’s performing on stage – then, in mid-song, asks the pub audience members to pass the beer up on stage, like a pint-sized bucket brigade. And they do, and McCartney accepts it happily.

“It was a really delightful, improvised, impromptu moment,” Ray recalled. “ It was a lovely moment. They’re pals. So that’s the kind of thing that pals do, and the cameras just happened to be there. It wasn’t planned or thought out.”

In 2016, The Late Late Show with James Corden won the Emmy as Outstanding Talk Show, and another Emmy for Outstanding Variety Special – for a prime-time “Carpool Karaoke” special featuring Jennifer Lopez and others. With summer 2018 airdates for both the original McCartney segment and tonight’s expanded special, it’s likely that Corden will be nominated again next year in both those categories. And just as likely he’ll win.

Yet the emotional impact of When McCartney Met Corden, like the title of tonight’s expanded CBS special, didn’t come from nowhere. Nor did Corden’s apparent bond with the former Beatle – and a look back at two British TV appearances, both of them predating Corden’s March 2015 debut as the new host of The Late Late Show, trace and explain these ties.

When Corden was appointed as Craig Ferguson’s Late Late Show heir apparent, it was a surprise appointment akin to Conan O’Brien being named as the Late Night successor of David Letterman. But, as it turns out, O’Brien was the longer shot by far, because no video of him as a talk-show host or interviewer existed. With Corden, it did – at least in the United Kingdom.

In May 2014, Corden was the host of a one-hour BBC 1 special in which he climbed into a car driven by a former boy-band member and went on a two-day tour, visiting the singer-songwriter’s first performance venue, his mother, and to a music rehearsal in the studio. In between, Corden and the former pop star talked, often very honestly and unguardedly, about fame, tragedies, life’s ups and downs, and the power of music.

The star in question was Gary Barlow. Both famous and infamous in the U.K., he and his former boy band, Take That, are much less familiar stateside (as is former bandmate Robbie Williams, a subsequent solo star in Britain in his own right). Think of Barlow as a U.K. version of Justin Timberlake, and you’ve got the general idea.

The one-hour special was called When Corden Met Barlow – and to Corden’s talk-show career in general, and the When McCartney Met Corden approach and structure in particular, it’s a shockingly precise blueprint. Watch:

That was in 2014. Three years prior to that, as part of a British charity fundraising special called Red Nose Day 2011, Corden reprised his abrasive character of Smithy from his 2007-10 British sitcom Gavin & Stacey. In a sketch he doubtlessly had a strong hand in writing, Corden appeared in a lengthy sketch in which he, as Smithy, is called in to help Red Nose Day up its national and international profile.

Three things to note about this particular video segment:

One is that it begins with Corden’s Smithy driving around with George Michael, and singing along, in gleeful duets, to some of Michael’s old hits from Wham! – the clear, original forerunner to “Carpool Karaoke.”

Another is that it’s full of unexpected, delightful celebrity cameos. Some of them, like Gary Barlow, won’t mean much to Americans, but others certainly will.

And the third is that one of those celebrity cameos is Paul McCartney, whose dialogue here is as perfectly delivered as it is written. It is, I suspect, where Corden and McCartney first connected, and developed the trust and collaborative energy that eventually led to the CBS special shown tonight.

Here’s the entire Corden Red Nose segment:

Watch these two videos, before or after seeing When Corden Met McCartney, and you’ll fully appreciate where it all originated: Corden as a talk-show host, “Carpool Karaoke” as a viral video staple, and Corden and McCartney as an enjoyably dynamic duo.

For all involved, the partnerships, and the music, continues. McCartney returned the favor recently by visiting Corden’s Late Late Show offices and taking a tour of Corden’s workplace (you’ll see it in the special). And as for music, there’s some now, and more coming very soon. Brian Ray has a new recording of “One Heartbeat,” the hit he co-wrote for Smokey Robinson in 1987, which features Robinson on guest vocals. And next month, Ray appears as part of the band on McCartney’s first studio album in years, Egypt Station – which includes music performed on When McCartney Met Corden. And on that special, the music spans from the early 1960s to the late 2010s, with all of it hitting chords that are more than just musical.

“There’s no sort of quantifying the impact of the canon of songs from Paul and John, George, Ringo, the Beatles, and then from each of them as solo artists, and Wings and all of their band projects as well,” Ray said.

“There’s just something that happens.”

Watch the faces of those surprised pub patrons at the Philharmonic, and you'll see it happen instantly.