Sir Paul McCartney pens astonishing love song to ex Heather Mills

But surely none could have predicted the former Beatle's first words about Miss Mills since the split would be so affectionate.

Sir Paul has made an extraordinary step towards peace by penning his former wife a love song. He has recorded the acoustic ballad My Soul in collaboration with Asian-influenced electronic music guru Nitin Sawhney.

Doomed romance: Sir Paul McCartney and Heather Mills in 2002, the year of their wedding

The track is to be released on Sawhney's new album London Undersound in October.

Its warmth towards Heather will surprise those who watched the increasingly acrimonious divorce between the couple come to a messy conclusion on the steps of the High Court earlier this year.

Sawhney said: 'Paul has done a track about how he feels about Heather and what was going on with the paparazzi because no one has heard his side of it at all  -  so this will be the first time anyone hears a song relating to that subject. It's very emotional and a very powerful song.'

In the song, Sir Paul sings sweetly about how Heather rescued him from the dark days after the death of his first wife Linda from breast cancer in 1998.

In tones full of lament and often cryptic lyrics, he also appears to place blame with others for being less than honest about their relationship and the paparazzi for their space being 'invaded'.

In the chorus, McCartney sings of how his soul and Heather's heart are now 'two worlds apart', adding perhaps a dream of how it could have turned out better for them both with the words: 'We could climb every mountain, swim through every sea. When the all world is asleep we could set ourselves free.'

In the verse beginning 'I long to know all your secrets' he appears to be saying that he would have helped her through her troubled past life if he had only known about it.

A string of colourful tales emerged about Miss Mills only after the couple's fouryear marriage broke down in 2006.

One persistent rumour for example  -  which has always been denied by Miss Mills  -  involved her being a high-class call girl. Soft porn images of her also came to light after the pair separated.

A friend of Sir Paul said last night: 'What the song shows is that rather than feeling embittered towards Heather, Paul just feels sorry for her.

'He feels sorry that she was never able to tell him the full truth about her past life. He feels that their romance happened so fast and so publicly that a lot never really got said.

'Paul knows Heather is a complex person, and deeply misunderstood  -  but that she has hardly helped herself by being less than transparent about her life.'