"I'd seen him a couple of times and thought, 'Wow, you know, he's an interesting looking guy,'" Paul McCartney tells BBC Radio 2
Credit: Courtesy Gunther/MPTV

Paul McCartney is opening up about the early days of The Beatles — and how he first spotted John Lennon on a bus.

"I'd seen him a couple of times and thought, 'Wow, you know, he's an interesting looking guy,'" McCartney, 78, tells Lennon's youngest son Sean Ono Lennon during a BBC Radio 2 special commemorating what would have been the Imagine songwriter's 80th birthday.

"And then I once also saw him in a queue for fish and chips and I said, 'Oh, that's that guy off the bus,'" adds McCartney.

"I'm talking to myself, in my mind I thought, 'I saw that guy off the bus, oh he's pretty cool-looking. Yeah, you know, he's a cool guy.'"

John Lennon and Paul McCartney
| Credit: AP

The teenage McCartney had no idea that the chance sightings would one day blossom into the greatest songwriting partnership of all time.

In fact, all he knew at the time was that he and Lennon shared a similar taste in the '50s 'Teddy Boy' fashion of long jacket, slicked-back hair, and drainpipe trousers.

"I knew nothing about him except that he looked pretty cool. He had long sideboards and greased back hair and everything…  it was the Teddy Boy look. All of us were trying to do a bit of that at that point, so if you ever noticed someone who was trying to do it you thought, 'I'll probably get on well with him,'" McCartney explains. "But I didn't know anything about him. And I didn't know who he was except that I'd seen him on the bus and I'd seen him in the fish and chip shop."

The Beatles
| Credit: Michael Ochs Archive/Getty

This all changed when a mutual friend called Ivan introduced Lennon to McCartney at a church hall fair on July 6, 1957, where John was performing with a band called The Quarrymen.

McCartney "got to sort of hang with them in the interval” and from that moment the songwriter's friendship blossomed, with Lennon regularly visiting McCartney's house to learn chords and practice.

While both hail from Liverpool, however, that doesn't mean they were cut from the exact same cloth.

Whereas McCartney had a large, friendly, music-playing family, Lennon had a much tougher early life, having been removed from his mother, Julia, at the age of 5 to live with his Aunt Mimi.

John Lennon
John Lennon
| Credit: J Kelly/Daily Sketch/Shutterstock

"It was only later when I realized... what a difficult upbringing he'd had compared to me," McCartney tells the BBC, adding that Lennon "idolized Julia and it was so sad that he wasn't living with her and his half-sisters."

Despite this, the Yesterday songwriter says that "Compared to the rest of us in the Beatles, [John] was the posh one," because he lived in a more upmarket neighborhood of Liverpool.

And while McCartney, Lennon, or their bandmates George Harrison and Ringo Starr never had any formal musical training, he actually feels it was an advantage because it forced The Beatles to learn to write, play and record music from the ground-up together.

"I look back on it now like a fan," adds McCartney. "I think, 'Wow. How lucky was I to meet this strange Teddy Boy off the bus who turned out to play music like I did, and we get together and, boy, we complemented each other.' You know, it was a bit yin-yang."

The Beatles
The Beatles

PEOPLE's new special edition, The Story of The Beatles is available now on Amazon and wherever magazines are sold.