"Pawn Stars" fan-favorite, Chumlee, is planning a private wedding later this year ... so he threw a party in Las Vegas to celebrate the forthcoming nuptials.

The party went down Saturday night in the Detroit Ballroom at the D Las Vegas in downtown Sin City. Chumlee and his fiancée, Olivia Rademann, welcomed some familiar faces to their party, including "Pawn Stars" honchos Rick and Corey Harrison.

The D Hotel Casino

Also in attendance were MTV stars Kailah Casillas and T.J. Lavin, who applauded as a slimmed-down Chumlee sliced into tiered wedding cake. D Casino owner, Derek Stevens and his wife, Nicole, congratulated the couple and wished them a happy life. There was also a magician walking around the party performing card tricks.

As we first reported, Chumlee popped the question last year during a trip to Hawaii. We're told they plan on returning to the islands in a few months to officially tie the knot in a private ceremony.

Chumlee has a lot to celebrate lately, especially his 100 lb weight drop after receiving gastric sleeve surgery. He's also been successfully running his own business in Vegas, Chumlee's Candy, located next to the famed Gold & Silver Pawn shop.