The couple enjoyed a night out in Las Vegas to celebrate Duhamel's sister's birthday

By Christina Dugan
Updated August 21, 2015 02:50 PM
Dimitrios Kambouris/Getty

Fergie and Josh Duhamel stepped out in true Vegas fashion to celebrate a special birthday this week.

On Thursday, the couple enjoyed dinner at Hakkasan in Las Vegas to celebrate Duhamel’s sister Ashlee’s birthday.

According to an onlooker, the intimate group of family and friends sipped on specialty cocktails and tucked into a number of the restaurant’s signature dishes.

“They were laughing with one another and toasting throughout the evening,” says the source.

After a few hours of feasting, the group made their way to TAO Nightclub, where they danced and took photos with each other at a VIP table.

At one point, Fergie made her way to the DJ booth with DJ Five and had him pause the music so she could lead the crowd in singing “Happy Birthday” to her sister-in-law, says a fellow partier.

Fergie Sings Happy Birthday to Josh Duhamel’s Sister

This won’t be the only birthday celebration the couple will mark this month. Their one-year-old son, Axl, will be turning 2 at the end of the month.

Reporting by MARK GRAY and MELODY CHIU