Bono is afraid of Alicia Keys.
While Keys talked about being pregnant and empathic when filming her documentary about AIDS in Africa, the U2 singer chimed in and said: "She's scary, isn't she? She's scary."
Bono went on to say that Keys has "lioness energy" and that her role as a new mother won't allow her to "let other mothers suffer."
He made the comments at the premiere of "Keep a Child Alive with Alicia Keys," a documentary which followed a visit to South Africa during last year's World Cup with a pregnant Keys and five Americans. It airs on Showtime on Dec. 1, which is World AIDS Day.
Bono said he met Keys when they recorded a cover of Marvin Gaye's "What's Going On" _ with dozens of other musicians _ in 2001.
"I was terrified the moment I met her. I was shaking in my boots," he said. "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."
Keys started her charity, Keep a Child Alive, in 2003. It assists those affected by HIV/AIDS in Africa and India.
She says she hopes the film reaches out to those who want to help, but can't make it to Africa.
"Even if you never have been able to travel there, or if you never can, that doesn't mean you can't travel with us and really see it for yourself," she said.
Bono says Keys has what it takes to make a difference in Africa, and around the world.
"Everyone's got heart, but actually you have to have the head for this," he said. "You have to be tough and strategic, you have to be demanding, (and) the money has to be spent well." If the money isn't spent well, he said, people get annoyed, "and so all these things take a certain intellectual rigor."
Keys has composed music for the Broadway play "Stick Fly," which debuts next week. When Bono _ who along with the Edge wrote the music for "Spider-Man: Turn off the Dark" _ was asked what advice he could give Keys, he said: "You know, it's an amazing American tradition, Broadway, and she can do anything she wants."
Mesfin Fekadu covers entertainment for The Associated Press. Follow him on Twitter at http://twitter.com/musicmesfin