Speaking to the BBC, she said: ““He has told me about it. And I know it exists. It’s happening.
“It’s been created by Kit as far as I can understand, so he’s in it from the ground up,” she continued. “So what you will be watching, hopefully, if it happens, is certified by Kit Harington.”
The sequel will reportedly pick up where the Game of Thrones series finale left off.
Harington’s portrayal of fan-favourite Snow earned him two Emmy nominations over the course of the series’ run, which began in 2011.
Adapted from George RR Martin’s hit fantasy novels, Game of Thrones is set to spawn several spin-offs, including the forthcoming House of the Dragon – slated for release in August this year.
The first trailer for the hotly-anticipated prequel was released in October last year and gave fans a look at several of the characters from the series.
Fans have already voiced scepticism about the prospect of a Jon Snow spin-off, with many citing the poorly recieived series finale of Thrones as an ominous sign.