Sienna Miller just wore one of Kate Middleton's favourite fashion brands

The actress was dressed like royalty.

sienna miller blue dress
(Image credit: Getty Images Photo by David M. Benett/Dave Benett/WireImage 1242287464)

The actress was dressed like royalty.

If, like us, you love keeping up with the Duchess of Cambridge's favourite fashion brands, then you'll know that Kate Middleton is a big fan of Self-Portrait.

In fact, the Duchess was spotted in a white Self-Portrait dress back in April, and it practically flew off the shelves. So, it's no surprise that lots of stylish celebrities have been following in the royal's footsteps and trying out the brand for themselves.

The latest celebrity to join the hype? None other than Sienna Miller.

That's right, the actress was just spotted wearing a light blue, knit midi dress by Self-Portrait to attend the red carpet premiere for The Sandman.

sienna miller blue dress

Getty Images Photo by David M. Benett/Dave Benett/WireImage 1242287258
(Image credit: Getty Images Photo by David M. Benett/Dave Benett/WireImage 1242287258)

Sienna's dress featured a statement bow-shaped bodice and fluted sleeves, and she paired it with simple white heels and a matching white shoulder bag. Perfection.

Her exact outfit is still available to buy, and we happen to think that it would make the perfect wedding guest dress.

Light Blue Lurex Knit Midi Dress, £370 | Self-Portrait

Light Blue Lurex Knit Midi Dress, <a href="https://www.self-portrait.com/products/light-blue-lurex-knit-midi-dress" data-link-merchant="self-portrait.com"">£370 | Self-Portrait
Awash in powder blue lurex knit for a metallic finish and sculpted fit, this midi dress is a photo-ready dream. Style it with nude heels on a night out in the city, or seaside cocktails on a weekend away.

If you're looking for a more affordable alternative, we've rounded up some of our favourite high street versions below. Just keep on scrolling...

Get the look: Sienna Miller's blue knit dress:

Rib-knit Cashmere-blend Dress, was £69.99 now £50 | H&amp;M

Rib-knit Cashmere-blend Dress, <a href="https://click.linksynergy.com/deeplink?id=kXQk6%2AivFEQ&mid=43250&u1=hawk-custom-tracking&murl=https%3A%2F%2Fwww2.hm.com%2Fen_gb%2Fproductpage.1058871001.html" data-link-merchant="www2.hm.com"">was £69.99 now £50 | H&M
This calf-length dress comes in a soft rib knit containing some cashmere and glittery threads. It features a round, trimmed neckline, dropped shoulders, long sleeves and a slit at one side of the hem.

Wide Rib Asymmetric Neck Knit Dress, was £69 now £28 | Warehouse

Wide Rib Asymmetric Neck Knit Dress, <a href="https://go.redirectingat.com/?id=92X363&xcust=hawk-custom-tracking&xs=1&url=https%3A%2F%2Fwww.warehousefashion.com%2Fwide-rib-asymmetric-neck-knit-dress-%2FBWW01566-106-34.html&sref" data-link-merchant="SkimLinks - warehousefashion.com"">was £69 now £28 | Warehouse
If you're looking for something a bit bolder, this bright blue number should do the trick. It features a flattering striped design and a slit at the hem for easy movement.

Ribbed Knit Dress, was £35.99 now £12.99 | Mango

Ribbed Knit Dress, <a href="https://click.linksynergy.com/deeplink?id=kXQk6%2AivFEQ&mid=36057&u1=hawk-custom-tracking&murl=https%3A%2F%2Fshop.mango.com%2Fgb%2Fwomen%2Fdresses-and-jumpsuits-midi%2Fribbed-knit-dress_27028647.html" data-link-merchant="shop.mango.com"">was £35.99 now £12.99 | Mango
With temperatures set to rise, why not go for a a sleeveless version? This Mango dress is made from a cable knit fabric with a midi design, ruched detailing in the neckline and and side ruffles.

We want them all.

Grace Lindsay

Grace Lindsay is currently Junior Beauty Editor at Who What Wear UK and previously was Marie Claire UK's E-Commerce Writer.  With over three years of experience in the fashion and beauty industry, she covers everything from the best make-up and skincare deals to how to shop the stand out trends of the season. When she's not typing away at her laptop, Grace can be found shopping her favourite vintage markets IRL, or catching up on her never-ending list of books to read.