Former South African President F.W. de Klerk (C) watches as U.S. President Barack Obama arrives to speak during a memorial service for Nelson Mandela at FNB Stadium in Johannesburg December 10, 2013. World leaders from Obama to Cuba’s Raul Castro joined thousands of South Africans to honour Mandela on Tuesday in a memorial that will celebrate his gift for uniting enemies across political and racial divides. REUTERS/Kevin Lamarque (SOUTH AFRICA – Tags: POLITICS OBITUARY) – RTX16C62