It's winter loving and they're having a blast! Over the weekend, Las Vegas lit up when former Grease star, Olivia Newton-John, hit the stage at the Flamingo Hotel and Casino. As the crowd watched the starlet's performance, they got a special surprise from Olivia's Grease co-star, Didi Conn. That's right! Sandy and Frenchie were back together! The two got into character to perform the films classic hit Summer Nights, but one thing was missing, John Travolta. Check out the video to see the epic reunion!.