Kelly first performed the piano ballad for the beloved leader, who died yesterday at 95, in Mandela's South African home in 2010.
The "Do What U Want" collaborator explained his feelings about the leader to Hall before the performance: "I sang for Nelson Mandela in his home, out in Africa, during the time when I was doing the  World Cup. And I sang a special song for him on his piano."
Kelly voiced a sentiment common to nearly all those who met Mandela. "I'm just blessed to know that I walked in his presence," Kelly said. "Being around him inspired me to even go further in my life in my walk and my career and everything, man. He's just an incredible power."
The performance is breathtaking, but difficult to watch. After an emotive introduction by Hall, the audience remains pin-drop quiet as Kelly's vocals soar and tremble, intertwined with sparse piano notes.
The song crescendos with these lyrics:
"He stood on the front line
He led the way
Out of the darkness
He didn't let us go astray
He was ready to die
For our sake
And that takes a soldier's heart."
The whole thing is pretty phenomenal. We dare you to remain dry-eyed after watching.