Posing with co-star, Javier Bardem, in a tiny black dress, boyfriend blazer and snakeskin heels, the 42-year-old's enviably long legs undoubtedly stole the show.
Julia is in Spain to promote her new movie but also to pick up the festival's Donostia lifetime achievement award.
We salute Ms Roberts for reclaiming the mini-dress and proving that you can flaunt it after 40 and still look fabulous. What do you think of the actress's look? Do you need legs like Julia's to get away with hemlines that short?