The star, who played Sansa Stark in the hit HBO series, was answering questions from fans live on her Instagram channel, when she suddenly stopped mid-sentence and ‘casually’ tossed the vape that was sitting in her lap on to the floor.
She and her hair stylist, who was working on Turner’s tresses at the time, both dissolved into giggles upon realising her awkward mistake.
Fans suspect that the small instrument was a weed vape due to comments she made at New York’s Comic Con 2018 in which she talked about smoking cannabis with fellow Game of Thrones co-star, Maisie Williams.
“We’re kind of like loners on Game of Thrones, just because the past few seasons Maisie and I have sleepovers every night when we’re shooting. Or every night whenever both of us are in town,” she said.
“We just used to sit there and eat and watch stupid videos and smoke weed.
‘We’d get high and then we’d sit in the bath together and we’d rub makeup brushes on our faces. It’s fun.
She then added: “I don’t know if my publicist will kill me for saying this.”
Williams was tipped to be maid of honour for Turner’s wedding to American singer Joe Jonas, but the couple were married in a surprise ceremony on 1 May this year, where Williams was not understood to be present.
Turner and Jonas married at A Little White Wedding Chapel in Las Vegas immediately after the 2019 Billboard Music Awards.
The service was officiated by an Elvis impersonator.
Earlier this week, Turner published a behind-the-scenes photograph to her Instagram page of Isaac Hempstead Wright (Bran Stark), Maisie Williams (Arya Stark) and her on the set of Game of Thrones.
In the picture, Turner is looking deep in thought while puffing on a vape, while Williams wears a pair of dark sunglasses and stares into the middle distance.
In sharp contrast to the women’s pensive expressions, Hempstead Wright can be seen smiling at the camera with a bottle of water balanced on his head.