Nicole Kidman and Keith Urban
06/22/2008 at 12:00 PM EDT
Talk about a surprise party.
After Keith Urban
sang "Who Wouldn't Wanna Be Me" for pregnant wife Nicole Kidman
, the country star announced to the Chicago Soldier Field crowd Saturday night that she just had a birthday the day before.
"So it would be nice to have 50,000 people sing 'Happy Birthday' to her," he said – and brought Kidman on stage for a stadium-sized sing-a-long for the actress, who turned 41
A surprised and glowing Kidman, in a long flowing black floral tank top dress, blew the audience a kiss and returned backstage when the song finished. The couple are awaiting the birth
of their first child, due any day.