Watch - Sir Paul McCartney stuns fans in emotional Carpool Karaoke in Liverpool

Sir Paul McCartney made a stunning appearance on Carpool Karaoke, reducing host James Corden to tears.

The 76-year-old former Beatle toured around his hometown of Liverpool, gifting viewers an incredible glimpse into his early life.

A visit to the famous Penny Lane was followed by a call at the singer's childhood home before the visit culminated in an emotional singalong at a city centre pub.

The segment started with Corden seated in his car before making a phone call and channelling one of The Beatles' best-known hits.

He said: "I'm in Liverpool, and I need your help. Yeah, I need somebody, not just anybody, please, please help me.''

Sir Paul then climbed into the passenger seat and the pair broke into a version of The Beatles' classic Drive My Car.

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.

During the conversation, Sir Paul revealed he wrote his first song at the age of 14, titled I Lost My Little Girl, before treating fans to a snippet.

Corden countered by saying that his first song, written with his school band, was called Girl Are You Ready.

The pair then drove to the historic Penny Lane, which inspired a song of the same name based on Sir Paul's experiences of growing up in the area.

As they made their way down the road, the song began to play on the radio and the former Beatle sang along before they left the car and the singer signed his autograph on the road sign.

Throughout their journey, he pointed out notable landmarks from his youth, including a church where he was once in the choir.

They stopped at the barbershop mentioned in Penny Lane and Sir Paul took selfies with the stunned staff.

Corden told him: "Your music is so full of positivity and joy and a message of love and togetherness, I feel like it's more relevant today than it's maybe ever been.''

The singer revealed that the band thought their music would only last 10 years and expressed his shock at its continued endurance.

He recounted the story of how he came to write Let It Be, saying a dream of his mother had inspired the song.

Corden labelled it "the most beautiful story'' he has ever heard, before the pair perform a version of it.

The Late Late Show host then began to cry and revealed that his grandfather and father once sat him down and played him Let It Be.

From there, they journeyed to the home where Sir Paul lived as a teenager in the Allerton area of Liverpool.

The rocker demonstrated how his music sounded better in the toilet - the acoustic chamber'' - while also showing where he and bandmate John Lennon would write songs.

Sir Paul then took Corden to The Philharmonic pub in Liverpool city centre, where drinkers were treated to a surprise gig.

He played A Hard Day's Night, Love Me Do, Back In The USSR and Hey Jude as members of the audience cried.

Sir Paul's Carpool Karaoke will air in the UK on Sky One at 10pm on Friday

You can watch it down below