The majority of the actor's fans will be used to seeing her with her natural brunette tresses, while portraying the role of runaway-turned-ruthless-assassin Arya Stark on the television show.
Now that the eighth and final season of the fantasy epic has come to an end, Williams has taken a step further away from the character she's played for almost a decade by going blonde.
On Monday, the day the finale aired in the UK, Williams shared a photograph on Instagram of her new blonde, fringed hairdo.
The 22-year-old captioned the picture with a single black heart emoji.
Several of Williams followers expressed their admiration for her new look.
"I LOVE YOU BLONDE!" one Instagram user commented.
"Proof that you suit every hair colour," another remarked.
This isn't the first time Williams has experimented with hair colour.
In early April, the actor attended the premiere of season eight of Game of Thrones in New York with a bold, lilac hairstyle.
Meanwhile, while attending Paris Fashion Week in March, the Cyberbully star sported a light pink dye job.
Just five days before posting her latest picture, Williams shared photographs on Instagram of herself with orange-tinged hair.
The most recent picture Williams shared on Instagram was taken by photographer Martin Mougeot for a new M+RC Noir fashion campaign.
The actor wears an M+RC Noir jacket in the shot over a forest green hoodie.
To read all about the significance of Sansa Stark's Game of Thrones finale look, click here.
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