Sophie Turner has revealed a dirty little secret from Game of Thrones.

The actress, who plays Sansa Stark in the hit HBO show, has revealed that for several seasons she wasn't allowed to wash her hair.

Stark told InStyle the rule came into place in recent seasons to portray the character's growth.

"For the first few seasons I was allowed to wash my hair because I was an aristocratic young girl," she said.

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"Towards season five, they started asking me to not wash my hair and it was really disgusting ... for a couple of years I was living with pretty greasy hair."

To make matters worse, Turner revealed particles from snow machines would get "stuck in the grease ... It was disgusting."

But Turner revealed they found a solution for filming of the last season - which begins airing here in April - as she was allowed to wear a wig.

Thrones' final season screens here from April 15.