Nick, who turned 21 today (16 September), held his glitzy bash at the Wynn hotel and was joined by his girlfriend Olivia Culpo, Danielle and his brother Kevin, and other brother Joe and his girlfriend Blanda Eggenschwiler.
Danielle, who is expecting a baby girl with Kevin, dared to flash some flesh in a LBD with a risqué sheer panel down the front.
The frock also had delicate beading around the shoulders and she teamed it with a pair of heeled shoes with an ankle strap. Kevin, meanwhile, was dressed in a grey suit and white shirt and he stood protectively with his arm around Danielle on the red carpet.
Birthday boy Nick wore a blue pinstriped suit and black shirt with checked pocket hankie and his girlfriend, who is Miss Universe 2012, showed off her model figure in a long purple bodycon dress.
Threatening to steal Nick's thunder, Joe turned heads in a monochrome leopard print shirt while Blanda stood out in a bright red pencil dress.
Nick was obviously excited about celebrating his birthday with his brothers and their other halves. Prior to the party, he tweeted: "Gearing up for my 21st in Vegas T minus 2 hours and 40 mins till party time.
Happy Birthday, Nick!
Do you like Danielle's dress? Tell us below, as the best comment from across the website each week wins £50.