The star was just 12 when she played Claudia in the 1994 Neil Jordan film and she admits she appreciated the way her two co-stars coddled her.
"They treated me like a little sister," she told "The Late Show with Stephen Colbert" host Stephen Colbert on Thursday, August 15. "I was very sweet. I was a very innocent 12-year-old. I was just doing my job and they were very sweet to me."
Kirsten, now 37, admits she was starstruck by Cruise and Pitt when she first met them.
"I did (know of their fame), but I was also very innocent," she explained. "I feel like I watched Brad in 'A River Runs Through It', and Tom was in 'Far and Away', which I loved."
And she was so taken by Brad's performance in "A River Runs Through It", she planned the name her firstborn after his character.
"I remember Brad in 'A River Runs Through It' and his name was Tristan and I was like, 'I'm going to name my first son Tristan' - you know, little girl stuff," she quipped.
Kirsten, who welcomed her first child last year (May 2018) with her fiance Jesse Plemons, ended up naming their son Ennis.