Soul singer Alicia Keys has hosted a star-studded charity event in London attended by some of the biggest names in showbiz.Keys founded and is the global ambassador for Keep A Child Alive, an organisation that helps to raise money for children and families with Aids.She made a trip to South Africa which she said inspired her to start the charity in 2003.Keys said she was "ecstatic" that stars Jennifer Hudson and Annie Lennox were among the musical performers at the charity event.But she wasn't the only excited celebrity on the red carpet.Following her on the arrivals line was Oscar-winner and friend Hudson, who said she was thrilled to be helping out with the charity ball."I am a big fan and a supporter, and of course any time someone needs some help I am there," Hudson said.She said people need to come together to help stop the epidemic.Other celebrity guests included actor and comedian Russell Brand and actress Mischa Barton.