There's a reason why Nicole Kidman and husband Keith Urban's marriage lasted this long-she's his biggest fan.

During the performance of "The Voice" coach at the Country Music Awards festival in Nashville, the 47-year-old actress can be seen backstage.

"The 47-year-old actress was spotted gazing lovingly at her husband as he performed live on stage at the final night of the Nashville music event, said Daily Mail. "She even appeared to be singing along to her favourite parts as she watched from the side of the stage."

The usually elegant Nicole Kidman wore a plaid shirt and dark skinny jeans to make sure she doesn't stand out from the crowd watching her husband Keith Urban perform. But she showed off her fashion flair by wearing a string of pearls around her neck.

"Urban put on a typically energetic performance dressed in a grey T-shirt and faded light blue jeans," the British publication added. "And his wife looked more than impressed as she smiled proudly as he gave it his all on stage."

Keith Urban later took to Twitter to thank his fans. "NASHVILLE!!!! It feels SO good to play in front of the home crowd! Thanks to everyone who came out.... -KU #CMAfest."

In an interview with Us Weekly, Keith Urban said that her marriage to Nicole Kidman works because he and the actress "are very in sync with the way we want to raise our girls."

"[We maintain] a very expressive, artistic house. I'm very comfortable with it," he said.

Keith Urban also said that the marriage means that he's now being outnumbered by women in the household but that's okay.

"I didn't grow up with any girls in my family, it was just my brother and me and mum and dad. Now being in a family that is all girls, I'm learning an enormous amount," he added.