Bono wrote a love song for his mother on U2's latest album.

The 54-year-old singer paid tribute to his mum Iris on the band's 13th studio album, 'Songs of Innocence', and admits the autobiographical theme of the record was ''excruciating'' to write because he was determined not to leave anything out.

He said: ''It's challenging stuff. What that meant was nothing, nothing was to be kept back. So you end up with a song about - I mean, how f***ing embarrassing is this? I write the lyrics to a song about my mother.

''It was like, 'Are you gonna go there?' So I went there. Here's a wild thing - my mother collapsed at her father's graveside 40 years ago yesterday and I've just sent out a love song to her.

''It's pretty excruciating stuff.''

Bono covered much of his early life in tunes on the album, including how he changed both ''mentally and spiritually'' after seeing The Clash perform live when he was younger.

He added to Q magazine: ''So we decided to go, 'Are you ready to write about the street you grew up in? Are you ready to write about your friendships that got you through things?

''Are you ready to write about going to see the Ramones when you found somebody else who sang like a girl and then you found somebody else who sang like a girl and then you felt you could be in a band?

''Do you remember playing [Dublin pub] The Baggot Inn and people shouting, 'More punk in the Monkees?' And then going to see The Clash and changing mentally, spiritually?' ''