The 45-year-old actress, who is playing the late Princess Grace in the new movie, was horrified at the conditions the extras had to deal with, so arranged for better facilities for the background cast, reported Star magazine.
"About 200 extras were forced to shoot late into the night in 40 F weather wearing only light clothing. Everyone was freezing. The next day Nicole demanded that tents be set up for the extras and they be supplied with warm blankets, hot food and coffee to keep them comfortable," said a source.
Kidman's kind actions prompted the extras to joke that the Australian beauty - who has children Isabella, 19, and Conor, 17, with ex-husband Tom Cruise, and Sunday Rose, four, and Faith Margaret, 23 months, with spouse Keith Urban - was just like a "real princess".
"It was like she was a real princess, barking orders and looking out for her people. And her caring actions were a real hit with everyone," the source said.