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 on Friday.

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.