Cyrus, 20, who wore Lil Kim-inspired costume that night, split with fiance Liam Hemsworth last month after the actor was said to be perturbed with the former teen star's raunchy performance at MTV Music Video, reported Ace Showbiz.
"They seemed really into each other. Soon they were flirting and talking very closely. Then they shared a kiss. They left Bootsy Bellows together around 1 A.M. They tried to be discreet by sharing a car with some other friends but it was clear they were leaving as a couple," a source said.
"They were dancing and just really getting into the spirit of things. Kelly didn't stay very long and so after catching up with Miley she left," the source added.