Singer Amy Winehouse Takes the Stage at Nelson Mandela's Birthday Show

Looking tan and radiant, Amy Winehouse on Friday sang at Nelson Mandela's 90th birthday concert in London in spite of health problems that have plagued her.

Winehouse, 24, has undergone numerous medical tests and spent time in the hospital in recent weeks after fainting at her home in London earlier this month. She has been photographed looking pale and sickly.

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But there were no signs of illness Friday night in Hyde Park when Winehouse took the stage in front of nearly 50,000 to perform hits including "Rehab" and "Valerie," London's Daily Mail reported.

Later, the blues songstress known for her heavy black eyeliner and jet-black beehive hairdo returned with Jerry Dammers and the Soweto Gospel Choir for a rendition of "Free Nelson Mandela" by The Special AKA.

At one point, Winehouse gave a nod to her husband, Blake, who is in prison, by replacing the lyrics with "Free Blakey, my fella," according to the Mail.

The concert was dubbed 46664 after Mandela's prison number, also the name of his AIDS charity, which will receive money raised by the birthday bash.

Among the other celebrities and performers were Annie Lennox; Will Smith and Jada Pinkett Smith; Leona Lewis; Razorlight; British Prime Minister Gordon Brown; and Sugababes, the Mail reported. Members of Queen closed the show with "We Are the Champions."

Click here for more on this story from London's Daily Mail.