Best birthday ever?

Casper Smart turned 25 on Friday -- and celebrated his first-ever birthday with girlfriend Jennifer Lopez that night, who surprised him with about 30 pals at Cecconi's, the celeb-friendly Italian eatery in West Hollywood.

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The sexy backup dancer was the guest of  honor at an "amazing" feast and party with 30 pals (including Lopez's fellow American Idol judge Randy Jackson) in the restaurant's Butterfly Room, according to one source.

"Jennifer made arrangements beforehand and made some special requests: steaks!" the source explained to Us Weekly of the meat-intensive meal. "Lots of champagne and steak!" Guests also noshed on chicken salad and shrimp salad before the main course.

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To treat her beau of over five months, the singer and designer, 42, also brought in a "huge special cake" from an outside bakery.

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Genuinely surprised, Smart was "so happy throughout the night," the insider added, noting that he and his world-famous girlfriend were kissing throughout the bash. "He was very touched. . . [Jennifer] really likes that guy."

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