The 'American Idol' judge took to the stage at his concert and told the audience he wrote the song 'Once In A Lifetime' in 2006 a day after talking with then-fiance Kidman about their upcoming nuptials, reported the Herald Sun.
"A couple of months before the wedding, we were in our hotel and we were talking about the future and Nic was getting very nervous about marrying me," Keith told the sold out crowd.
"She was saying things like 'It's a long shot' (but) I knew she loved me and was just nervous. I did everything I could to remind her that I was going to be her man forever," he added, before performing a rendition of the song for his wife.