Jess recently chopped her hair into a graduated lob (that's a long bob, FYI), but appeared to be rocking an even shorter style at the Nina Ricci autumn/winter '14 show.
But although it seems like the Sin City actress had a drastic cut, we reckon her new barnet is actually down to some clever styling.
Jess was in the capable hands of hairdresser Carlos Ferraz, and it looks like he tucked her hair into a 'faux bob'.
Bobs are huge right now, but if you're too scared of lopping off your lengthy locks then a faux bob is a great way to try out the look (without the commitment!)
Fancy giving it a go? Here's how:
1. Volume is key, so boost your barnet with a mousse (like Bumble & Bumble Thickening Full Form Mousse, £21.50, boots.com). Apply to your roots post-wash, then blast with your hairdrier until dry.
2. Create a side parting, then take a wide barrel curling wand (like Remington Pearl CI9532 Pro Curl Hair Styler, £27.99, boots.com) and tong large sections to form tousled waves. Once finished, gently brush out your curls for a more natural look.
3. Next, pull your hair back into a loose ponytail and secure with a thin hair elastic.
If your hair is already quite short then place your hair tie near the ends of your tresses. If it's long, place it half-way between the nape of your neck and the tips of your hair.
4. Now for the tricky part! Tuck the end of your ponytail under, towards your neck, until it forms a bob-like shape. Secure with bobby pins (you'll need quite a few!)
5. Pull out a few strands at the front to help frame your face, then fix your bonce in place with hairspray (try Mark Hill Get Gorgeous! Fabulous Finish Hairspray, £5.99, boots.com).
But if that all sounds a bit too complicated, try simply tucking your mane into a high round-neck jumper. All the fashionistas are doing it...
What do you think of Jessica's hair? Let us know by commenting below as the best comment across the site each week wins £50!
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