The 37-year-old actress wore a heavy velvet purple floor length gown to the 70th annual festival to the Jaeger Le Coultre gala dinner in Venice on Monday night (2 September) and we're not sure what we make of it.
The former model did glow with simplistic makeup wearing her hair slicked back showing off some spiked diamond-drop earrings standing side by side with her long-term boyfriend of seven years Joshua Jackson.
Although neither of them were promoting a film, Diane can be seen in the current series The Bridge on FX on Wednesday nights.
What do you make of Diane's gown? Tell us in the comments below as the best comment from across the site each week will win £50!