Another insider adds that the couple (who publicly split in February 2009 after Brown's infamous assault of Rihanna) were seated near Jay-Z's wife Beyonce plus singers Rita Ora and Santigold.
"Don't Wake Me Up" singer was spotted kissing Rihanna's cheek, and kept his around her. "They weren't looking like they were expecting people to be shocked at all," the first source says. "Totally casual about it."
Adds the second insider: "They looked full on back together."
Earlier that evening, both Rihanna and Brown were photographed -- separately -- leaving the Ganservoort Hotel, where the "S & M" chanteuse has been staying.
Making their reunion even more complicated? For over a year, Brown has been dating model Karrueche Tran, with no news of a confirmed split between the pair. After Brown and Rihanna were spotted earlier this week making out at an NYC club, Tran angrily tweeted, "There's a difference between a man and a boy." She added, "I prefer men."