President Barack Obama headed to South Africa on Monday to speak at a national memorial service for anti-apartheid icon Nelson Mandela. He was joined on Air Force One by former President George W. Bush and former Secretary of State Hillary Rodham Clinton. Obama and his wife, Michelle, boarded the plane under cold, rainy skies for the long flight. Bush and his wife, Laura, and Clinton, already were on board.

Former President Bill Clinton was traveling separately from Rio de Janeiro, where he was attending a Clinton Global Initiative event. And former President Jimmy Carter also planned to join the group in Johannesburg. George H.W. Bush is the only living president who will not attend. His spokesman said the 89-year-old no longer is able to travel long distances.

The American leaders will join dozens of other dignitaries and tens of thousands of mourners at the memorial service at a Johannesburg stadium. Mandela will be buried Dec. 15, after a state funeral in his hometown of Qunu.