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Justin Timberlake

Rob Loud/WireImage

Sounds like Justin Timberlake may be celebrating his last days as a single man.

We just got word that Jessica Biel's hubby-to-be may have had his bachelor party in Las Vegas last night.

The Trouble With the Curve star was spotted dining at Sinatra Restaurant at the Wynn before hitting Surrender Nightclub at Encore with about 20 friends.

They were even decked out in what was described as Rat Pack-themed suits, a possible ode to Timberlake's love of the ole Hollywood gang.

And that's not all. Timberlake and his group of buddies, which included his producer pal Timbaland, also took over a dance floor table at Tryst, also inside the Wynn, where resident DJ Spider was spinning the beats. Ryan Seacrest was also in the house, but not with Timberlake.

Earlier in the day, Timberlake was spotted relaxing poolside at Surrender inside a VIP cabana.

It's still not 100 percent clear if all this fun was Timberlake's bachelor bash, but one source says it was. We'll let you know as soon as we hear more!

Timberlake's rep did not immediately comment.