Jennifer Lopez was treated to a lavish birthday party on a yacht by her boyfriend Casper Smart.

The 43-year-old star was whisked off to a pier on Manhattan's west side by her 25-year-old lover on last night (24.07.12), where Casper and her manager Benny Medina had arranged a party with her closest friends and family.

A source told Usmagazine.com: "She was so surprised! All of her close friends and family were there, and there were silver balloons and fresh flowers everywhere.

"The cake was a teddy bear because her and Casper call each other 'Bear'!' and he gave her a necklace with a tiny pink diamond teddy bear on it."

The couple were joined by guests including Mary J. Blige but they only had eyes for each other.

The source added: "Jennifer was kissing Casper and he was by her side all night. She really had the best time!"

The singer-and-actress started dating her back-up dancer last autumn just a few months after her seven-year marriage to Marc Anthony ended in July 2011 but he has recently insisted there were no romantic sparks between the two of them initially.

When asked by if it was love at first sight when the pair met, Casper said: "I don't think it was, for either of us. It was just very natural, you know, natural how it happened.

"There was nothing before, no flirting, no nothing."