Analysis of information sources in references of the Wikipedia article "Fifth Beatle" in English language version.
Sir George Martin is often regarded as 'The Fifth Beatle.' ...
Called "the Fifth Beatle" Preston also worked with other musicians, including the Rolling Stones, Eric Clapton, and Sly and the Family Stone
The man they call the Fifth Beatle, who 'fell in love with art' at Prescot Grammar School, is to have work displayed in a charity exhibition. ...
Sir Paul McCartney said of him: 'If anyone was the Fifth Beatle, it was Brian.'