Former Beatle Sir Paul McCartney's hit ballad Yesterday was "influenced" by a Nat King Cole track, music experts have said.
Sir Paul said the tune came to him in a dream in 1965
Sir Paul said in 1965 that he awoke in his London flat with the tune for Yesterday in his head and asked friends if they recognised it.
They said they thought it was his melody and that it had come to him in a dream.
Now, music experts have said the song - which has been covered by more than 2,000 artists and played on the radio at least six million times - have been subconsciously influenced by the song Answer Me.
It was recorded by Frankie Laine, David Whitfield and Nat King Cole.
Musicologist Spencer Leigh told BBC Radio 4's Today programme he did not think Sir Paul had plagiarised the tune, but that it had been an influence on his famous hit.
The Beatles (Paul McCartney left) did not recognise the melody
"I think he would have heard it when he was 10 or 11, he certainly would have known the song.
"McCartney said he woke with this wonderful melody in his head, and he felt it had come from somewhere else," Mr Leigh said.
However Sir Paul's spokesman told BBC News Online: "To me the two songs are about as similar as Get Back and God Save the Queen."
Sir Paul had played the track to the other Beatles and to their producer, George Martin, just after he wrote it but they could not name anything similar.
The songwriter had originally planned to call the song Scrambled Eggs, but then changed it to Yesterday, giving the song a more sombre, reflective mood.
The crooner Nat King Cole had a hit in the 50s with Answer Me
The song begins with the line: "Yesterday, all my troubles seemed so far away/Now I need a place to hide away".
Answer Me has the line: "Yesterday, I believed that love was here to stay, won't you tell me where I've gone astray."
Mr Leigh said: "George Martin didn't point out it was similar [to Answer Me], if he had, I think McCartney would have changed his tune."
Mr Leigh's views have been echoed by musicologists Alan Clayson and Dominic Pedler.
"There are some uncanny similarities: the overlap of lyrics, the multiple rhyming emphasis on words ending with 'ay', the similar scan of the songs, Mr Pedler told the Sunday Times.
"McCartney didn't hijack the song, but he must have been inspired by it," he said.