In a break with Carpool Karaoke tradition, the veteran singer then took the wheel and drove Corden - who appeared visibly starstruck - around the streets of Liverpool. They also sang the music icon's new songs "Come on to Me" and "I Don't Know", which will be featured on his album Egypt Station (out September 7).
After getting back in the auto, Corden says Sir Paul's music is "so full of positivity and joy", and "more relevant now today than it's maybe ever been".
"So, I wrote the song, 'Let It Be, '" McCartney concluded. Their duet left Corden in tears: "That's the power of music", said McCartney.
McCartney made it even more poignant when he told Corden: "He is".
They then leave the auto to visit the barber's shop mentioned in the song - leaving the owner in sheer disbelief.
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As part of the video, the pair embarked on a journey around McCartney's hometown, visiting Penny Lane and his family home, which he saw for the first time in 50 years.
"Hi, I'm Paul McCartney", he said (needlessly) introducing himself to the homeowner.
The segment climaxed with Paul returning to one of the pubs Paul used to play before The Beatles hit the big-time, surprising the locals with a performance with his current band - singing hits decided by the audience via a jukebox. After playing a mini-concert, Paul then finishes with "Hey Jude" - because really, any Beatles fan would be hard-pressed to find a better way to end the day than by singing along to the song's iconic chorus, especially if it's Paul McCartney you're singing along with. The TV personality gushed, "I think this is an afternoon none of us will forget".
Help! James Corden needs somebody... to show him around Liverpool, England.