Paul McCartney
The singer said the incident nearly made him quit.
The Queen Bey put her spin on the track, now titled Blackbird, on her latest album Cowboy Carter.
“It sort of fits if you look at the lyrics..."
"I was just like, smelling his cologne, and I started like, breathing in the same rhythm as him," the Golden Globe winner told Jimmy Kimmel.
"I’m very thankful – but I’ve also been driven up the wall by it..."
British musician sang on the Moody Blues hit Go Now and co-wrote Mull of Kintyre.
The Beatles' Now And Then has topped the UK charts – and made music history.
The Fab Four unveiled their "final" song, Now And Then, last week.
Paul McCartney and Ringo Starr unveiled new single Now And Then on Thursday afternoon.
"It's quite emotional and we all play on it, it's a genuine Beatles recording," Sir Paul McCartney said.