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It's been a banner few weeks for Jessica Biel: "Valentine's Day" is a hit; she climbed Mount Kilimanjaro; and she's tighter than ever with Justin Timberlake, whose mom has even started dropping hints about grandkids.

It might not be a bad time for her to buy a lottery ticket.

On Wednesday, the starlet played proud girlfriend as the chart-topper presented his William Rast clothing line at New York Fashion Week, cheering him on from her primo seat in the front row, located right next to his parents.

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She's "one of us," enthuses Justin's mom, Lynn Harless, to People magazine. "She's amazing. She's so down-to-earth and her family is great."

And counter to recent rumors that the pair's three-year romance had hit a rough patch, "They're always trying to out 'special' each other," adds Lynn. "They're pretty openly affectionate."

That was certainly the case at the post-show shindig at Hudson Terrace, where E! News says Timberlake and Biel were joined at the lips for much of the evening.

The chart-topper did come up for air long enough to hop onstage and belt out a tune, which made the female-heavy crowd go "wild," according to the New York Post. After the performance, Justin immediately sought out his squeeze, who was standing by a red velvet curtain.

"He opened the curtain and stepped Jessica behind it, then wrapped them in it before giving her a long kiss," relays a spy.

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Seems that was just the opening act. A little later, they headed upstairs, where the real action began.

"He ended up giving her a lap dance," says an eyewitness. "It was pretty raunchy."

And just in case the PDA didn't convincingly prove that all is well for the pair, Justin's mother offers up a bit of stork-baiting.

"I've had friends who have grandchildren and I've tried to express to him that I'm losing that race!" she laughs to the mag, although she's quick to point out, "They're young. They have plenty of time."

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Timberlake, 29, must have given his mom the green light to gush about his relationship with Biel, 27, because he was apparently concerned about the possibility of flapping gums at his fashion show.

"Justin made everyone sign an agreement not to gossip about him," a source alleges to the New York Post. "Then, three-quarters of the entire venue was closed off for him, so all the stylists were forced to work on 31 models in a tiny area, causing tempers to flare."

Despite the apparent space issues, the presentation was a hit, earning critical kudos, along with the highest compliment Vogue overload Anna Wintour can give: She reportedly removed her sunglasses to get a better look at the collection's denim, fringed, military and leather designs.

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