A crowd of about 46,000 celebrated Nelson Mandela’s 90th birthday on Friday at a party held for the South African Nobel Peace Prize winner in London.

Twenty years ago, a similar concert was held to celebrate Mandela’s 70th birthday and to raise awareness of his imprisonment.

Even though he looked frail as he was leaning on his wife’s arm, Mandela spoke with optimism about his attempt to raise awareness about AIDS, the disease that is mostly encountered in African countries.

“Where there is poverty and sickness, including AIDS, where human beings are being oppressed, there is work to be done,” he said in his speech. “Our work is freedom for all.”

Despite his optimism, Mandela reminded the public that “our work is far from complete” and that there was still a lot of work to be done.

The name of the charity, 46664 Campaign, represents Mandela’s prison number when he was incarcerated at Robben Island. All proceeds from the concerts, for which there were 46, 664 tickets, are going to the above mentioned campaign against AIDS.

Musicians such as Leona Lewis and Amy Winehouse, and bands including Razorlight and Queen participated in the outdoor show in London’s Hyde’s Park, which was hosted by movie star Will Smith. Josh Groban and the Soweto Gospel Choir also performed at the concert.

Mandela praised all the musicians present at the celebration, saying their “voices carried across the water” inspired “us in our prison cells far away.”

“We are honored to be back in London for this wonderful celebration, he added.”

Mandela was released from prison in 1990, after spending 27 years in jail, and was elected South Africa’s first black president in 1994. He retired from politics in 1999.