The 38-year-old actress took to Instagram to share a makeup-free selfie, showing off her flawless skin and proving that she's only getting better with age.
"I don't know why I still look like a teenager sometimes," she captioned the bare-faced pic, adding the hashtags #sky, #nomakeup and #thegoodolddays.
It looks like the blonde beauty has found the fountain of youth, but what's her real secret?
"Sunscreen," she told InStyle back in 2013. "I started getting brown spots when I first moved to L.A., and coming from Europe I wasn't so accustomed to the sun. Now I wear SPF 50 or 60, even when it rains."
Joshua Jackson's longtime love also revealed she "wasn't blessed with great skin."
"I used to have rosacea and had to quit smoking to get rid of it," she said. "I still struggle with undereye circles. It's all about discipline and finding products that are right for you."
Another beauty secret? "I've noticed my skin looks better when I don't drink, so I stopped for six weeks before the Cannes Film Festival," she explained. "It did me wonders. I slept better than ever. It kind of sucked, though, because I enjoy a glass of wine."
What do you think of Diane's makeup-free snap? Sound off below!