Donning a floor length black gown with a high slit and plunging neckline, Carey, 46, dazzled as she accessorized with fishnet stockings and flashy diamond earrings, bracelets and a matching necklace.
The singer, who wore her blonde locks in loose curls, attended the event with fiancé James Packer although it seems the two arrived separately, as Carey made her entrance surrounded by bodyguards.
The mother of two also shared some personal shots from the night, taking to Instagram to congratulate the host.
“Great job Leo,” she captioned a photo of herself with DiCaprio, adding a kissy face emoji.
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DiCaprio’s annual gala aims to raise funds that will support environmental awareness efforts and research on climate change, conservation and preservation grants across the world. Last year the event raised $40 million.