Keith Urban thinks Nicole Kidman is ''extraordinary, pure and a beautiful light.''

The Australian country singer - who previously credited his wife with helping him to overcome his drug addiction - paid a heart-warming tribute to the 'Grace of Monaco' actress before performing his track 'Once In A Lifetime' during his concert in Sydney today (21.06.14), and revealed she was initially worried about marrying him in 2006.

Speaking on stage, the 'American Idol' judge - who has daughters Sunday, five, and Faith, three, with Nicole, said: ''I want to make a special dedication, about this time eight years ago we were about five days away from getting married.

''A few days before that my fiancée and I were talking about the wedding and she was worried about getting married to me - understandably - I was trying every way I could to reassure her that I was born to be her man ... the only thing I could do was reassure her, comfort her, be strong.

''The next day, I happened to be with a friend of mine who was a songwriter and I was telling him what happened and he said we should write about that so I wrote this song for my wife and she's here tonight.''

The 46-year-old singer added: ''In a world of so much darkness and toxicity and scary people, she is extraordinary, pure and a beautiful light and I love you with all my heart baby girl.''

Nicole, 47, attended the star-studded gig with her parents, according to the MailOnline.