On the eve of Jennifer Lopez's 43rd birthday party, boyfriend Casper Smart surprised the singer with a big birthday bash aboard a yacht in Manhattan's Chelsea Piers.

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As onlookers reported that Casper led the former American Idol judge on the boat blindfolded and surprised her with a crowd of friends and a big, white bear birthday cake.

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Jennifer looked fantastic in a slinky, backless orange Tom Ford dress and red stilletos.The duo will celebrate their one year anniversary this November.