Christina Aguilera Stuns in Stylish Black Dress at Monaco Gala

Christina Aguilera let the genie out of the bottle for a gala fundraiser in Monaco ... showing off her figure in a black dress with a plunging neckline.

The singer-songwriter pulled up to the Prince Albert II of Monaco Foundation's 20th anniversary gala at the Opéra de Monte-Carlo on Friday ... looking her best.

She donned the aforementioned dress ... with a huge shiny choker hanging from her neck.

Christina looked as much like royalty as the actual prince and princesses there ... drawing eyes at the event, which also included Monaco's Prince Albert II and Princess Charlene.

While the star looked serene, she didn't have the night off ... she actually performed at the gala -- with Plácido Domingo and Sister Sledge also taking the stage. Monica Bellucci and Richard Gere were the guests of honor.