On May 05, 1999, Britney Spears performed at the World Music Awards, which were held in Monaco.
She performed ...Baby One More Time, and also performed The Beat Goes On, as a tribute to Cher, who also performed that night, and who received the Legend Award. Janet Jackson was the other recipient of the Legend Award during that ceremony.
Other performers of the night included Ricky Martin, Alejandro Sanz and Tarkan.
There's some interviews of Britney while she was in Monaco