South Africa's former president Nelson Mandela will turn 90 on July 18, but despite his retirement from the public eye five years ago, his age has never prevented him from being pushed back into the limelight.

Political, business and showbiz elite from around the world arrived in London to greet South Africa's long-imprisoned champion of anti-apartheid with a fund-raising concert on Friday, June 27.

British Prime Minister Gordon Brown, former United States President Bill Clinton, talk-show queen Oprah Winfrey, Academy Award winning actor Robert De Niro and former James Bond actor Pierce Brosnan were among the stars joining Mandela in the British capital.

The Mandela birthday celebration will be capped with a concert at Hyde Park on Friday that will feature Annie Lennox, Queen, Razorlight, Leona Lewis and the Soweto Gospel Choir.

The proceeds from the concert will go to Mandela's 46664 Foundation that looks after people suffering from HIV in his beloved South Africa.

Mandela was imprisoned for a total of 27 years by a then predominantly white South African government until the abolition of apartheid in the country.

In a sweeping change of the political landscape in the wealthiest country in the African continent, Mandela was elected as the first black president of the country in 1994.

Mandela said before members of media that, though he may be retired, he still works for his suffering people and he wants to take advantage of his landmark birthday to raise funds for his charity work.

Mandela criticizes Robert Mugabe

Former South African President Nelson Mandela criticized Zimbabwe's President Robert Mugabe, labeling him a "tragic failure of leadership." Mandela expressed his sadness over the political and economic chaos that now rocks South Africa's biggest neighbor, to its north-west.

The former anti-apartheid leader broke his silence while in London after hearing of accounts that opposition leader Morgan Tsvangirai withdrew from the scheduled next phase of the run-off presidential elections in Zimbabwe.

Mandela's statement is expected to put pressure on his successor, President Thabo Mbeki, to finally speak out against Mugabe.