Lucy Morris's batmitzvah party was in full swing at the Village Hotel, Elstree.
As guests got down to a track by American rapper Fatman Scoop, there was a surprise. So much so that party organisers Genie Events hadn't even planned it.
"Suddenly Fatman Scoop appears and takes the mike," said Genie's Mark Starman.
The singer, who had been staying at the hotel after appearing in Celebrity Big Brother, had been spotted in the lobby by the batmitzvah's uncles.
"He was extremely pleasant and really interested in what a batmitzvah was," said Lucy's father, Simon. "Next thing we knew he was marching into the main room and was on stage performing his signature song."