The 36-year-old actress sported a pretty grey mini, natty brogues and a chic fedora for film producer Joel Silver's annual holiday shindig in Malibu yesterday.
On the arm of long-term boyfriend Joshua Jackson, the Chanel favourite looked relaxed and summery as she made her way into the party at Mr Silver's home where she no doubt hob-nobbed with fellow guests Gwen Stefani and her husband Gavin Rossdale.
We've said it before and we'll say it again - what we would give to rifle through Diane's wardrobe. On and off the red carpet, she gets it right every single time.
For more summer-inspired outfits, check out our shopping gallery geared towards the sunshine season.