The two stars were enjoying time together in Telluride, Colorado, when they came to the aid of another skier.
An onlooker said, "Justin and Cameron had been on the slopes and were going down a red run when they saw someone bang into this brunette. And she went flying."
"Everyone just looked on shocked as she landed in a heap on the ground screaming with pain and it looked as though she had broken her legs."
"No one had any idea the couple who dashed to help her were Cameron Diaz and Justin Timberlake until 20 minutes later when they took their hats and masks off to meet the paramedics who’d turned up."
"They were amazing and you’d never have thought they were so famous."