A Wind from the North is a short story announced by Garth Nix on his Twitter and Facebook accounts in May 2015. In 2017 Nix stated that the story was turning into a novella.  In 2018 he confirmed that he was still working on the story, and it was about 80% done.  In 2020 Nix confirmed the short story now formed part of his upcoming novel Terciel and Elinor. 
The story will be "about how Sabriel's parents first met, amongst other things."