The 33-year-old British actress was wining and dining with her fiancé Tom Sturridge at Chiltern Firehouse (the name check celebrity haunt in London right now) on Wednesday night minus the signature long tresses.
Check out this photo that Mary Charteris posted on Instagram of Sienna and Lily Allen hanging out ahead of Dolly Parton's headlining act. Note the wavy down 'do.
Hands down, the shorter look is the winning one.
As for Sienna's date night outfit? She played it low-key in a pair of grey skinny jeans, a slouchy cream jumper with gold embellishment on the sleeves and metallic peep-toe ankle boots. We'll also be doing the multiple stud earrings thing too.
LOVE SIENNA'S STYLE? Take a look through this gallery to see more sexy-making ensembles from the Brit beauty.
MORE! Watch all the latest news on Sienna right here.