Beyonc Knowles and her husband Jay-Z "seemed to really have fun" together at a private event this week.

The pair welcomed daughter Blue Ivy into the world in January.

Beyonc and Jay-Z recently took a holiday with the baby on the island of St. Bart's.

Back in New York City, the couple are still in an extremely festive mood and decided to make a surprise appearance at a Cartier party Thursday night.

"Beyonc was doing a little dance [while Jay] smoked a cigar [in their private section]," an onlooker told Us Weekly magazine.

"They were very sweet together. They seemed to really have fun!"

Despite delivering Blue Ivy just three months ago, Beyonc is getting back into pre-baby shape rapidly.

The star stunned partygoers with her beauty at the function.

"She had on no make up, or very little," another observer detailed.

"She looks unbelievable. She seems to be about a size six now."

The couple tied the knot in 2008 but they have been together over 10 years.

Beyonc and Jay-Z are reportedly planning to renew their vows this year.