The actor, who plays Williams' on-screen sister Sansa Stark, posted a video to her Instagram immediately after the HBO show's latest episode was broadcast.
Williams later posted a voice message sent to her by an excited Turner.
*Major spoilers below - you have been warned*
It was Arya who ended up saving Westeros by defeating the Night King. Using the valyrian steel weapon given to her last season – and given a prophetic nudge by Melisandre – Arya ensured the universe lived to fight another day.
"You really are that motherf***ing bitch," Turner exclaimed. "You are that bitch. She did that."
While Turner was happy with the outcome, Williams revealed she was initially reluctant to believe that fans would accept it was Arya who got to kill the show’s most fearsome villain.
This twist came as a shock to Kit Harington who has said he believed his character, Jon Snow, would be the one to save the day.
The intense trailer for next week’s episode sees everyone turn their attention to the Iron Throne and the fate of Cersei Lannister.
The final season of Game of Thrones continues every Sunday.
Our extensive ranking of every character in the series – from worst to best – is below.
The show will be available on Sky Atlantic and NOW TV in the UK.
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