U.S. first lady Michelle Obama walks with Graca Machel, the wife of former South African President Nelson Mandela, as she visits the Nelson Mandela Foundation in Johannesburg on Tuesday, June 21, 2011. (AP Photo/Charles Dharapak, Pool)

Photo by: Charles Dharapak

U.S. first lady Michelle Obama walks with Graca Machel, the wife of former South African President Nelson Mandela, as she visits the Nelson Mandela Foundation in Johannesburg on Tuesday, June 21, 2011. (AP Photo/Charles Dharapak, Pool)