The John Lennon at 80 special will air in two parts on BBC Radio 2 and BBC Sounds on October 3 and 4. Lennon's birthday is Oct. 9.
The special is reportedly hosted by Lennon and Yoko Ono's son Sean Ono Lennon, who conducts interviews with his father's former Beatles bandmate McCartney, his godfather Elton John and his half-brother Julian Lennon.
Sean broaches the topic of songwriting with McCartney, and Sir Paul picks up a guitar and plays a section of a song called "Just Fun," which he says was one of the first songs he and Lennon ever wrote together, circa 1957.
"Just Fun" was mentioned in the 1970 Let It Be film, having supposedly been written one day when Lennon and McCartney skipped school.
"There were a few songs that weren't very good ... you know, clearly young songwriters who don't know how to do it," McCartney recalled. "Eventually, we started to write slightly better songs and then enjoyed the process of learning together so much that it really took off."
Elsewhere in the documentary, McCartney looks back on his first meeting with Lennon and the serendipity of their partnership.
After airing, John Lennon at 80 will be available via BBC Sounds for 30 days.
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