The Beatles - 'Here Comes the Sun' (found cut guitar solo of song; 1969)
In 1969, when The Beatles were recording their final proper album, "Abbey Road", during the recording of the track 'Here Comes the Sun', guitarist George Harrison performed a guitar solo that was cut from the released track. This solo went unheard for years until it was discovered during a recording demonstration by George Martin, Paul McCartney, and Dnhani Harrison in the 2011 documentary George Harrison: Living in the Material World. Due to strict policies on The Beatles' material being uploaded to the internet, it can be hard to find online. The documentary is available on platforms such as Amazon, however.