In a January 2015 appearance on the show, Kidman revealed she used to have a crush on Fallon and told a story about how the comedian missed an opportunity to ask her on a date.
Kidman returned to the late night talk show to discuss her new film, Lion, but instead told Fallon that he had another chance to ask for her number while the two were at a party at director David Fincher's house, but he didn't take it.
"It was a long time ago," Kidman revealed, saying the second encounter took place while Brad Pitt and Jennifer Aniston were still married. "You could have asked for my number then... and you still didn't ask for it!"
Fallon seemed embarrassed that he didn't remember the second opportunity either.
Kidman then surprised Fallon with an appearance by her husband, Keith Urban.
"I get it, I get it," Fallon said.