The duo were spotted getting cozy at the Empire Polo Club in Indio, California on Saturday, April 11, reported Ace Showbiz.
The couple began dating in 2013 and reportedly broke up last month.
40-year-old Cooper and 23-year-old Waterhouse were spotted hanging out at the star-studded affair with some friends. They later got close and shared embrace.
Some other celebrity couples who were spotted at the annual music festival, among others, were actor Robert Pattinson and his singer fiance FKA twigs, Ian Somerhalder and Nikki Reed, Lea Michele and her boyfriend Matthew Paetz, as well as Kate Bosworth and her husband Michael Polish.