Jennifer Lopez Engagement Ring? Singer Sporting Diamond on Ring Finger (PHOTO)

Jennifer Lopez has reignited rumors of an engagement after being photographed flaunting a large diamond ring on her ring finger while out in Paris with her boyfriend Casper Smart.

Lopez, 42, and 25-year-old Smart have reportedly been inseparable all week long while shopping and attending fashion shows in what is renowned to be the most romantic city in the world. Her diamond ring has prompted speculation that Smart may have proposed.

"He's madly in love with her," a source told US magazine about Smart, who will join Lopez on the European leg of her tour in October. "It's not just that she's his lover, she's also his best friend."

Lopez, a mother of two, began dating Smart, who works as a backup dancer, shortly after separating from her estranged husband, Marc Anthony, in July 2011.

"Jennifer and Casper spend all their spare time together – and he is crazy about [her] twins," a source told Star magazine. "He's a great substitute dad, and the twins love to play with him. They're already like a family."

The former "American Idol" judge has received some criticism about the 18-year age gap between her and Smart, who has playfully been dubbed her "boy toy" by various media outlets. Despite being referred to as a cougar, Lopez insists that age is an irrelevant factor in their union.

"Until somebody brings it up, I don't think we really think about it," the singer told talk show host Katie Couric. "We're just two people who have similar interests and love a lot of the same things and who get along."

Smart previously took to social networking site Twitter in January after the criticism evidently became overwhelming for the pair.

"Age, status, n opinions of others are irrelevant. Our hearts are endless and our souls infinite...To be continued," Smart tweeted.

"Our ages are mere reminders of the hours logged on this earth and the precious time remaining...To be continued," he wrote.

"We should all honor our time here by indulging our passion and dreams. So, close your ears and open your hearts; Love and be happy!" he later added.

To see photos of Jennifer Lopez's ring click here: