The 51-year-old actress recalled in the Jan. 21 issue of People the moment she knew Urban was the love of her life and her future husband.
"It was my [38th] birthday, and he stood outside with gardenias at 5 a.m. on my stoop in New York," she recounted. "That is when I went, 'This is the man I hope I get to marry.'"
Urban's romantic gesture came less than six months after he met Kidman at an event in Los Angeles in 2005.
"It was pretty intense," the actress said. "I believed by that point he was the love of my life. Maybe that's because I am deeply romantic, or I'm an actress, or I have strong faith as well, but I just believed, 'Oh, okay, here he is.'"
Kidman and Urban married in June 2006 and are parents to two daughters, 10-year-old Sunday and 8-year-old Faith. The pair looked the happy couple in new photos on Christmas Eve in December.
"Wishing you love, laughter and joy," Kidman captioned one picture on Instagram.
"Merry Christmas everyone - thank you all for ALL the love this year. We send love to every one of YOU!!!!! - us," Urban wrote on his own account.
Kidman and Urban attended the Golden Globe Awards together Sunday, where Kidman was nominated for Best Actress in a Motion Picture - Drama her role in Destroyer. She will return as Celeste Wright in Season 2 of the HBO series Big Little Lies.