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Jennifer Lopez and backup dancer Casper Smart performed and toured together before becoming romantic a few weeks ago -- and on Sept. 24, an eyewitness observed the undeniable spark between Lopez, 42, and Smart, 24, at a post-concert bash at Pure Nightclub in Vegas.

"They were flirting," the witness tells Us Weekly. "Casper even came over and gave her a lapdance. She was giggling as he gyrated on her." (Honey 2 star Smart also dances at L.A. hotspot Club Boulevard where he's "popular with the ladies because he goes shirtless!" according to a source.)

Get more scoop on the status of Lopez and her boytoy in this week's Hot Stuff video, as explained by Senior Editor Ian Drew with special guest, legendary rock chanteuse Nico (portrayed by performer Tammy Faye Starlite).

Also in the roundup: Cameron Diaz and Diddy's surprising fling, Ashton Kutcher and Demi Moore's last-ditch effort to save their marriage (at Bruce Willis' house!) and more.

Watch the Hot Stuff video now!