Spoiler: Bella opted for TRIPLE denim.
It's the question that divides the nation: Should you or shouldn't you double up on your denim?
Here at GLAMOUR, we're of the firm opinion that twice the denim = twice as good.
And if Gigi Hadid's 24th birthday party is anything to go by, its a look that's only growing in popularity.
Enlisting all her friends - and family - to arrive decked out in the trend, we were treated to quite the masterclass in how to do double denim.
Scroll down from some serious inspiration, from some of the chicest celebrities styling the look...
Gigi Hadid showcased her love for a doubled-up look, ensuring everyone at her 24th birthday arrived wearing it. Her lightly distressed, vintage-feel look is giving us all the Britney Spears/Justin Timberlake 2001 feels.
Bella actually one-upped her sister (at her birthday! Brave...) by opting for TRIPLE denim. We're into it.
We know... it's not technically double denim. But it's a denim dress - that counts, right? Olivia Culpo thinks it does.
Another bender-of-the-rules, Ashley Graham opted for a belted denim jacket as a dress. Well if it looks this good...
Mila Kunis is QUEEN of effortless dressing, but her double denim expertise is a particular sight to behold. The slightly different tones... the structured jacket with the ripped jeans. She can do no wrong.
Supermodel Gigi Hadid doesn't put a foot wrong by matching her double denim with this incredible red boots. Gimme.
Diane Kruger gives us lessons on how to make double denim look so so chic.
Zoë Kravitz has NYC street style nailed. We adore her double denim look - impeccable 90s cool.
Gwen Stefani is so cool she can get away with just about anything, including this awesome double-denim ensemble. Top marks, Gwen!
Wow, we love love love Dakota Fanning's double denim skirt and crop combo; the blue sunglasses by Quay Australia are super cool and complement her outfit to perfection. Make like her for a low-key yet ultra stylish day time look.
At a Guess event in Sydney, model Gigi Hadid rocked the double denim look marrying two different shades. Perfect.
Even in LA's summer heat, Rachel Bilson works the trend. We love her cute buttoned up shirt.
We love the patchwork detailing on Kendall Jenner's jeans. The model adds an extra western touch to her double denim in the form of a cool studded belt.
Jessica Hart looked stunning wearing double denim in New York. The model styled the look with a leopard print tee, Prada tote and off-duty sandals.
Kate Hudson looks picture perfect teaming her double denim combo with simple pumps and a neutral tote. When double denims done right, it really is one of the best looks...
Attending an event at AOL Studios in NYC, Anne rocks two-tone Double D effortlessly. We're digging her booties too.
DB gives the DD trend his seal of approval, teaming a light denim shirt with distressed jeans. He's even colour coordinated his bootlaces to his jumper for extra marks.
Katie Holmes works the perfect look for those who are new to double denim: team your denim jacket with grey or black jeans and you will feel less like you are wearing a Canadian tuxedo but will feel effortlessly cool. Also big plus points to Katie for the Adidas Stan Smith shoes.
Reese is working a slightly more polished version here with her black skinny jeans and blue denim shirt. Add a slick of pink or red lipstick and you're good to go.
Kate Bosworth wears different shades of blue to great effect.
If a look works, why not wear different versions of it? ‘Repeat offender’ Bosworth looks super cool. We're a little bit jealous of the chunky silver necklaces and that awesome dip dye shirt.
J-Lo works her typical high octane glamour with figure-fitting denim shirt and jeans, aviator shades and stacks of silver jewellery. Very nice.
Like Jennifer Lopez, Kim Kardashian has opted to accessorise her look with some nude high heels. However, she's chosen to finish her look with a salmon coloured coat – robed of course, because that’s what you do if you're into fashion in a big way.
To be fair, Miranda Kerr would look amazing if she wore a hessian sack but we are so totally in love with this classic denim shirt and jeans ensemble; and leopard print works a treat with blue jeans.
Rosie Huntington-Whiteley has noted this too and has accessorised her outfit with a gorgeous leopard print bag.
With her distressed jeans and white pointy stilettos, street style queen Jessica Alba gives a nod to the 80s – and it works.
Olivia Munn’s tan accessories look great with her faded denim top and jeans. She looks pretty pleased with herself... and so she should.
Here is another classic look: wear a white T-shirt with your denim and add these cute suede ankle boots (once again, not jealous at all) for some serious cowboy cool.
Chloe Sevigny can do no wrong in our books and she looks her usual cool in the hot Coachella dessert in this chic denim ensemble.
Here's a tip: A trend is not a trend worth pursuing if it hasn’t been worn by Alexa Chung at some point. However, Pixie is no slouch in the style stakes, she's working Madonna circa 1987 and that can only be a good thing.
Although we're not entirely convinced by Pixie’s footwear, we adore her double denim co-ord suit.
How awesome does Olivia Palermo look here? If you're not rushing out to buy a denim skirt right now, then double denim might really not be the right thing for you.
If Olivia’s outfit is a bit too Upper East Side New York for you, then Rihanna’s bad ass take on the look might be more your thing.
The denim waistcoat might not be everyone’s cup of tea but it has a very firm place in the history of rock music attire; that’s why we applaud Kristen for giving it a whirl.
Who better to demonstrate this than our very own Status Quo. Would you ever guess that they had a sponsorship with Levi’s at the time?!
Another rock staple is the cut-off denim jacket and Brian Johnson of AC/DC is working a particularly fine 80s number here.
How could we discuss music and denim and not mention Debbie Harry? Her ice queen look in the late 70s pretty much set the blueprint for every front woman in a band ever since.
It’s Elvis! *faints*
Speaking of cool dudes, Robert Redford casually striding down the street in 1976 is totally nailing that look.
In the same year, Charlie’s Angels chain themselves up and wear matching denim shirts and flare jeans. What's not to love?
The 70s were really a vintage decade for denim and we just have to include this awesome picture of Susan George and Peter Fonda in 1974 in Dirty Mary Crazy Larry.
Here's Robert Redford (again) in the romantic western The Electric Horseman. He plays a (hot) cowboy. Enough said.
Drew Barrymore working denim the grunge way in 1991. This outfit has 'cool' written all over it.
No ode to double denim would be complete without this (erm) gem. JT and Britney got it all wrong but we kind of love them for it.
Author: GLAMOUR