Sir Paul McCartney could not work for a year following the death of his first wife Linda, the musician has revealed.
A working version of Ecce Cor Meum was performed in 2001
The loss halted work on his fourth classical album, Ecce Cor Meum, which he started in 1997 and is released on Monday, Sir Paul told Classic FM.
"I had to take a year out just to grieve," he said, adding that was followed by a "big burst of sad music" that features in the piece.
Linda McCartney died from breast cancer in 1998. The couple had wed in 1969.
"There is an interlude in the middle of Ecce Cor Meum which is a very sad piece of music," said Sir Paul.
"My colleague and I remember actually sitting at the keyboard just weeping when we were doing this piece. It does it to me every time.
"It was a very, very emotional, very sad time for me, obviously, losing Linda."
Ecce Cor Meum, an oratorio in four movements with English and Latin lyrics, was recorded earlier this year at Abbey Road Studios in London.
It was commissioned by Magdalen College, Oxford, in honour of the college's new music hall.
The work will have its live premiere at the Royal Albert Hall on 4 November.
It is Sir Paul's fourth classical album following 1991's The Liverpool Oratorio, Standing Stone in 1997 and Working Classical in 1999.