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Now, she’s made another big switch. And her latest look? It’s just as chic and effortlessly cool.
The 33-year-old actress has farewelled her signature blonde, and welcomed in a rich, red shade just in time for autumn (she lives in the UK, remember).
Considering how popular her blonde lob was, we're predicting women the world over will start replicating this new look with equal enthusiasm. After all, Sienna Miller is nothing if not a trend setter — she was single-handedly responsible for many of those ubiquitous boho trends of the mid-noughties.
Miller introduced us to her new look at the London launch party for her sister's Debenhams fashion line, Nine by Savannah Miller.
Miller has coloured her blonde hair for her role in The Lost City of Z, which she's been busy shooting in Northern Ireland.
If you need any more temptation to book in for a chop or new colour, check out a few of our other favourite celebrity hair changes of late: