"Congratulations to the most beautiful pregnant woman in the world. You're gorgeous," Hilton said as she took the microphone at a party Aguilera was hosting early Sunday at LAX Nightclub.
Aguilera and her husband, music marketing executive Jordan Bratman, have never publicly confirmed they are expecting their first child, although baby rumors have been swirling for some time.
As Hilton made the announcement about Aguilera’s expecting, the singer buried her head into her husband’s shoulder while their friends appeared shocked, People.com said.
The couple then looked at each other and laughed as the news was greeted with applause.
Aguilera and Bratman have been married since 2005.