"David arrived first and then Roger came on and I saw Roger give David a hug," said organizer Bella Freud. "It was really lovely."
Gilmour and Waters warmed up for the unannounced, short set by sound checking "To Know Him Is to Love Him," "Comfortably Numb" and "Wish You Were Here."
"There were about 30 people milling about," Freud says. "Everyone was just stunned."
Gilmour and Waters were originally planning to play three songs. But one attendee, British financier Arpad Busson, was so taken with the performance, he ponied up a sizable donation to get them to play "Another Brick in the Wall, Pt. 2."
"People were crying — really! I know it sounds corny, but it was magic. David and Roger — they looked so happy up there and they made something so beautiful happen," Freud said.
Rolling Stone has reported that Waters has said he asked Gilmour to join 30th anniversary tour for The Wall, but Gilmour was "uninterested" in the offer.