The -year-old actor, who will next be seen in the film "Early Man", said the end of the hit HBO series will take away her "safety blanket" but she is game for newer challenges.
"I'm currently filming for the final season, which is all a bit weird. It's been my entire career.
"It's exciting now that I can do more things like this ('Early Man') and really shape my career to things that I want to do, but it's a little bit nerve-wracking because this has been my safety blanket and safety net," Williams said on the show "Lorraine".
"I was 12 when I got the part. I juggled both work and school at the same time for a while, but it was such an intense schedule.
"I went through school and GCSEs, but my character only got bigger and bigger so I was home-schooled for a little while and it was a strange little time. It feels ages ago now," she said.
"Game of Thrones" does not return until 2019.