Bono was "terrified" the first time he met Alicia Keys.

The U2 star was supporting Alicia yesterday at the premiere of her documentary, Keep a Child Alive with Alicia Keys.

The film follows Alicia and five Americans as they travel to South Africa during last year's soccer World Cup.

It airs on the Showtime channel on December 1, which is World AIDS Day.

Bono first met the songstress in 2001 when they recorded a cover of Marvin Gaye's classic song What's Going On.

"I was terrified the moment I met her. I was shaking in my boots," he said in an interview with USA Today. "I was very moved by her singing of course, but what was interesting was the hard questions afterwards, and I think it's those hard questions that she asks that lead her."

Alicia started the charity Keep a Child Alive in 2003. It assists those affected by HIV/AIDS in Africa and India.

Bono was full of praise for Alicia and said she has "lioness energy".

He said it takes a great deal of intellectual skill to run your own charity successfully.

"Everyone's got heart, but actually you have to have the head for this," he explained. "You have to be tough and strategic, you have to be demanding, the money has to be spent well. So all these things take a certain intellectual rigor."