Bono has spoken about how his voice changed after losing his father.

The U2 singer, who has been promoting his new memoir Surrender: 40 Songs, One Story (out November 1), has said in a new interview that he believes his voice opened up after his father, Bob Hewson, died from cancer in 2000.

Bono, whose real name is Paul Hewson, told NPR this week that the loss of his father, whom he had a tumultuous relationship with, actually changed the way he sings.

Referring to it as an “unscientific theory… [a] folksy idea that when someone you love passes on”, the singer explained that he feels strongly about his voice’s development in the wake of his father’s passing.

“My voice opens up,” he told NPR, “and there’s a physiological reason for that too because if you’re more relaxed as a person, your voice does open up.”

He added: “In the last few years I’ve been singing in ways I never could have imagined.”

Bono also spoke about his father telling him that he was “a baritone who thinks he’s a tenor”. When asked by the interviewer on what that might mean about his personality, he said that it’s an analogy to ambition and “punching over my weight”. He said: “I’m only interested in punching over my weight.”

Elsewhere in the interview Bono opened up about his faith, the values of which he described as Judeo-Christian, but likened it more to a general feeling of spirituality rather than being bound by religious practise.

He said, too, that he’s written some U2 songs in a gospel style, such as ‘I Still Haven’t Found What I’m Looking For’ from 1987’s ‘The Joshua Tree’.

Additionally, he ruminated on the reason why the word “surrender” is in the title of his new book, beginning by saying that he is naturally combative and was born with his “fists up”.

“I need to be more silent and surrender to my band; it’s been at the core of what I’m trying to do with my life. [I need to] surrender to my wife, surrender to, you know, our maker. These are not things that come easy to me.

“And when I say ‘surrender’, I do not mean making peace with the world. I’m not ready to make peace with the world. I’m trying to make peace with myself, I’m trying to make peace with my maker, but I’m not trying to make peace with the world. The world is a deeply unfair place, and I’m ready to rumble. I’m keeping my fists up for that one.”

In his book he also talks about discovering that his cousin is also his half-brother, the alleged death threats he’s received in his life, and the 2014 controversy in which U2 arranged for their album ‘Songs Of Innocence‘ to be automatically downloaded onto the devices of 500million iTunes users.